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1. What is the primary focus of Environmental Chemistry?
ⓐ. Synthesis of new organic compounds.
ⓑ. Study of the chemical processes occurring in the environment.
ⓒ. Analysis of materials used in industries.
ⓓ. Exploration of extraterrestrial chemical compositions.
Correct Answer: Study of the chemical processes occurring in the environment.
Explanation: Environmental Chemistry is an interdisciplinary branch of science that deals with the chemical and biochemical phenomena that occur in natural places. It involves studying the sources, reactions, transport, effects, and fates of chemical species in the air, water, and soil environments. Its main goal is to understand how human activity and natural processes affect the chemical makeup of the environment and to find solutions to environmental problems like pollution.
2. Which layer of the atmosphere is closest to the Earth’s surface, extends up to approximately $10{ km}$ at the poles, and contains all the air that living organisms breathe?
ⓐ. Stratosphere
ⓑ. Mesosphere
ⓒ. Thermosphere
ⓓ. Troposphere
Correct Answer: Troposphere
Explanation: The Troposphere is the lowest layer of the atmosphere, extending up to about $10{ km}$ at the poles and $20{ km}$ at the equator. This layer is where all weather phenomena occur and is where living organisms exist. Pollution in this layer is known as Tropospheric pollution. The Stratosphere is the layer above it, extending up to $50{ km}$, and is home to the protective ozone layer.
3. Environmental pollution is defined as the effect of undesirable changes in our surroundings that have harmful effects on plants, animals, and human beings. Which of the following is NOT classified as a major segment of the environment in environmental chemistry?
ⓐ. Hydrosphere
ⓑ. Lithosphere
ⓒ. Biosphere
ⓓ. Cosmosphere
Correct Answer: Cosmosphere
Explanation: In the context of environmental chemistry, the environment is typically studied in four major segments: Atmosphere (air), Hydrosphere (water bodies), Lithosphere or Pedosphere (soil/earth), and Biosphere (living organisms interacting with the other three). The Cosmosphere or outer space, being external to the Earth’s systems, is generally not considered a segment for studying chemical pollution on Earth.
4. Which of the following is the most suitable example of a biodegradable pollutant?
ⓐ. DDT (Dichlorodiphenyltrichloroethane)
ⓑ. Plastic materials
ⓒ. Domestic sewage
ⓓ. Heavy metal salts (e.g., Cadmium)
Correct Answer: Domestic sewage
Explanation: Pollutants are classified based on their decomposition rate. Biodegradable pollutants are substances that can be rapidly broken down by natural biological processes (like bacterial action) into simpler, harmless substances; domestic sewage (containing organic waste) is a classic example. DDT, plastic, and heavy metal salts are examples of non-biodegradable pollutants which persist in the environment for long periods.
5. A substance present in nature, but whose concentration has significantly increased due to human activity to a level that causes adverse effects on living organisms and the environment, is termed a:
ⓐ. Pollutant
ⓑ. Contaminant
ⓒ. Receptor
ⓓ. Sink
Correct Answer: Pollutant
Explanation: A pollutant is defined as any substance, which may or may not be naturally occurring, whose concentration in the environment is high enough to cause adverse effects on humans, animals, plants, or property. For this level of study, the presence of a substance at an abnormally high, harmful concentration is the key definition of a pollutant, distinguishing it from a substance at its natural, non-harmful level.
6. The primary difference between tropospheric pollution and stratospheric pollution is based on:
ⓐ. The chemical nature of the pollutants (gaseous vs. particulate).
ⓑ. The source of the pollutants (natural vs. man-made).
ⓒ. The altitude/atmospheric layer where the pollution occurs.
ⓓ. The effects of the pollution (warming vs. cooling).
Correct Answer: The altitude/atmospheric layer where the pollution occurs.
Explanation: The major distinction is the location. Tropospheric pollution (e.g., smog, acid rain) occurs in the troposphere (the lowest $\approx 10{ km}$), where pollutants are generated and remain due to air movements. Stratospheric pollution (e.g., ozone depletion) occurs in the stratosphere ($\approx 10$ to $50{ km}$), primarily affecting the ozone layer.
7. Which of the following is considered a secondary pollutant?
ⓐ. Carbon Monoxide (${CO}$)
ⓑ. Sulphur Dioxide (${SO}_2$)
ⓒ. Peroxyacetyl Nitrate (PAN)
ⓓ. Lead compounds
Correct Answer: Peroxyacetyl Nitrate (PAN)
Explanation: Pollutants are classified as primary or secondary. Primary pollutants are directly emitted from the source (e.g., ${CO}$, ${SO}_2$, Lead from vehicles). Secondary pollutants are formed in the atmosphere by chemical reactions between primary pollutants and other atmospheric constituents. Peroxyacetyl Nitrate (PAN) is a key component of photochemical smog, formed by the reaction of hydrocarbons and nitrogen oxides in the presence of sunlight.
8. The term ‘Sink’ in environmental chemistry refers to:
ⓐ. A region in the environment where a pollutant is produced.
ⓑ. The region of the environment where a pollutant undergoes degradation or removal.
ⓒ. Any living organism that is sensitive to a pollutant.
ⓓ. The process of pollutant transfer from one medium to another.
Correct Answer: The region of the environment where a pollutant undergoes degradation or removal.
Explanation: A Sink is defined as the region or process where a pollutant is removed from the atmosphere, water, or soil, or where it undergoes a chemical transformation into a less toxic or harmless form. For example, oceans are considered a sink for carbon dioxide (${CO}_2$), and rain-out processes act as a sink for atmospheric pollutants. A Source is where the pollutant is generated.
9. A major harmful effect associated with the presence of non-biodegradable pollutants in the environment is:
ⓐ. Eutrophication of water bodies.
ⓑ. Simple oxidation in the atmosphere.
ⓒ. Rapid breakdown by microbial action.
ⓓ. Biomagnification or Bioaccumulation in the food chain.
Correct Answer: Biomagnification or Bioaccumulation in the food chain.
Explanation: Non-biodegradable pollutants (like DDT and heavy metals) cannot be broken down by biological processes. Consequently, their concentration increases progressively at each successive trophic level in a food chain, a process called Biomagnification or Bioaccumulation. This high concentration in top predators, including humans, causes severe health problems. Eutrophication is related to excess biodegradable nutrients.
10. The depletion of the stratospheric ozone layer occurs primarily due to the catalytic decomposition of ozone (${O}_3$) by free radicals released from which class of compounds?
ⓐ. Oxides of Sulphur (${SO}_{{x}}$)
ⓑ. Oxides of Nitrogen (${NO}_{{x}}$)
ⓒ. Chlorofluorocarbons (CFCs)
ⓓ. Particulate Matter (PM)
Correct Answer: Chlorofluorocarbons (CFCs)
Explanation: Chlorofluorocarbons (CFCs), when transported to the stratosphere, are broken down by powerful UV radiation to release chlorine free radicals, ${Cl}^{\\bullet}$. These radicals catalyze the destruction of ozone (${O}_3$). A simplified reaction cycle is:
$${Cl}^{\\bullet} + {O}_3 \rightarrow {ClO}^{\\bullet} + {O}_2$$
$${ClO}^{\\bullet} + {O} \rightarrow {Cl}^{\\bullet} + {O}_2$$
The net reaction is ${O}_3 + {O} \rightarrow 2{O}_2$, where the ${Cl}^{\\bullet}$ radical is regenerated and can destroy thousands of ozone molecules.
11. Which term correctly defines the substance that causes an undesirable change in the environment, primarily by interfering with the natural biogeochemical cycles?
ⓐ. Pollutant
ⓑ. Contaminant
ⓒ. Receptor
ⓓ. Sink
Correct Answer: Pollutant
Explanation: A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. This term is reserved for substances whose concentration reaches a level that causes adverse biological or environmental effects, fundamentally disrupting natural cycles like the Carbon or Nitrogen cycle (e.g., excess ${CO}_2$ or ${NO}_{{x}}$). A contaminant is a substance not usually present, but not necessarily harmful.
12. Pollutants are classified based on their formation into primary and secondary pollutants. Which of the following correctly describes a secondary pollutant?
ⓐ. It is released directly from an identifiable source, such as a factory smokestack.
ⓑ. It is formed by chemical reactions between primary pollutants in the atmosphere.
ⓒ. It is an artificially synthesized substance that has no natural counterpart.
ⓓ. It undergoes biodegradation rapidly under natural conditions.
Correct Answer: It is formed by chemical reactions between primary pollutants in the atmosphere.
Explanation: Secondary pollutants are not emitted directly. They arise when primary pollutants (e.g., ${NO}_2$ or unburnt hydrocarbons) react with each other or with natural atmospheric components, often catalyzed by sunlight. Examples include Ozone (${O}_3$) in the troposphere, ${Peroxyacetyl Nitrate (PAN)}$, and formaldehydes. Primary pollutants, like ${SO}_2$ and ${CO}$, are emitted directly from sources.
13. Considering the rate of degradation, which of the following is the best example of a non-biodegradable pollutant?
ⓐ. Human and animal excretory wastes.
ⓑ. Vegetable and fruit peels.
ⓒ. DDT (Dichlorodiphenyltrichloroethane)
ⓓ. Paper waste
Correct Answer: DDT (Dichlorodiphenyltrichloroethane)
Explanation: Non-biodegradable pollutants are substances that cannot be decomposed or broken down by microorganisms or other natural means within a reasonable timescale. ${DDT}$ is a persistent organic pollutant (POP), which accumulates in the environment and undergoes biomagnification in the food chain, causing long-term harm. Options A, B, and D are all examples of biodegradable waste, which decompose easily.
14. The term in environmental chemistry that describes the component of the environment (like the atmosphere, soil, or water) which gets affected by the pollutant is known as the:
ⓐ. Source
ⓑ. Pathway
ⓒ. Pollutant itself
ⓓ. Receptor
Correct Answer: Receptor
Explanation: A receptor is the object, organism, or component of the environment that is adversely affected by the pollutant. For instance, if an industrial ${SO}_2$ plume causes acid rain, the atmosphere is the medium, and the lake or marble monument that suffers damage is the receptor. The source is where the pollutant originates, and the pathway is how it travels to the receptor.
15. What is the most significant environmental outcome resulting from the chemical reaction: ${CH}_4 + 2{O}_2 \rightarrow {CO}_2 + 2{H}_2{O} + {Energy}$?
ⓐ. Global Warming
ⓑ. Ozone Depletion
ⓒ. Acid Rain Formation
ⓓ. Eutrophication
Correct Answer: Global Warming
Explanation: The reaction shown is the combustion of methane (${CH}_4$), a potent greenhouse gas, which produces carbon dioxide (${CO}_2$), another primary greenhouse gas. The resulting increase in ${CO}_2$ concentration in the atmosphere enhances the greenhouse effect, leading to the gradual rise in the Earth’s average temperature, known as Global Warming. Ozone depletion is primarily caused by ${CFCs}$, and acid rain by ${SO}_2$ and ${NO}_{{x}}$.
16. Which among the following gaseous components is NOT generally considered a primary pollutant in the context of photochemical smog formation?
ⓐ. Nitric Oxide (${NO}$)
ⓑ. Ozone (${O}_3$)
ⓒ. Sulphur Dioxide (${SO}_2$)
ⓓ. Unburnt Hydrocarbons (e.g., ${RH}$)
Correct Answer: Ozone (${O}_3$)
Explanation: A primary pollutant is emitted directly from a source. While ${NO}$, ${SO}_2$, and unburnt hydrocarbons (${RH}$) are directly emitted from vehicles and industries, Ozone (${O}_3$) in the troposphere is formed as a secondary pollutant. It is created when ${NO}$ (primary) reacts with ${RH}$ (primary) in the presence of sunlight, a key step in photochemical smog.
17. Which natural reservoir is considered the largest sink for atmospheric carbon dioxide (${CO}_2$)?
ⓐ. Living Terrestrial Plants (Biosphere)
ⓑ. The Earth’s Soil (Lithosphere)
ⓒ. Oceans (Hydrosphere)
ⓓ. The Stratosphere
Correct Answer: Oceans (Hydrosphere)
Explanation: A sink is a long-term reservoir for a pollutant. The oceans are the largest active sink for atmospheric ${CO}_2$. ${CO}_2$ dissolves in water to form carbonic acid (${H}_2{CO}_3$) through the equilibrium: ${CO}_2({aq}) + {H}_2{O}({l}) \rightleftharpoons {H}_2{CO}_3({aq})$, which then further dissociates. While the biosphere and soil also act as sinks, the vast volume and solubility capacity of the oceans make them the largest long-term carbon sink.
18. What is the fundamental difference, in terms of effect, between a substance being a contaminant and a pollutant?
ⓐ. A contaminant is always biodegradable, whereas a pollutant is non-biodegradable.
ⓑ. A contaminant is only naturally occurring, while a pollutant is man-made.
ⓒ. A pollutant is always a liquid or solid, while a contaminant is a gas.
ⓓ. A pollutant causes measurable harm or adverse effects, while a contaminant may simply be present at an unusual place or concentration without causing harm.
Correct Answer: A pollutant causes measurable harm or adverse effects, while a contaminant may simply be present at an unusual place or concentration without causing harm.
Explanation: The terms are often used interchangeably, but chemically, a contaminant is a substance not usually present in a medium (like a foreign chemical). A pollutant is a contaminant whose concentration is high enough to produce detrimental biological or environmental effects. Therefore, all pollutants are contaminants, but not all contaminants are pollutants.
19. The major gaseous primary pollutant responsible for the formation of acid rain is:
ⓐ. Sulphur Dioxide (${SO}_2$)
ⓑ. Carbon Monoxide (${CO}$)
ⓒ. Methane (${CH}_4$)
ⓓ. Ozone (${O}_3$)
Correct Answer: Sulphur Dioxide (${SO}_2$)
Explanation: Sulphur Dioxide (${SO}_2$) and Oxides of Nitrogen (${NO}_{{x}}$) are the main precursors of acid rain. ${SO}_2$ is oxidized in the atmosphere to Sulphur Trioxide (${SO}_3$), which then reacts with water vapor to form Sulphuric Acid (${H}_2{SO}_4$).
$${SO}_2 + \frac{1}{2}{O}_2 \xrightarrow[{Dust particles}]{{Ozone/Hydrocarbons}} {SO}_3$$
$${SO}_3 + {H}_2{O} \rightarrow {H}_2{SO}_4$$
This reaction forms the major component of acid rain, lowering the ${pH}$ of rainfall.
20. Which category of pollution is characterized by the excessive accumulation of nitrates and phosphates in surface water bodies, often leading to the excessive growth of algae?
ⓐ. Thermal pollution
ⓑ. Atmospheric pollution
ⓒ. Eutrophication (Water Pollution)
ⓓ. Noise pollution
Correct Answer: Eutrophication (Water Pollution)
Explanation: Eutrophication is a form of water pollution caused by the excessive loading of nutrients, primarily nitrates (${NO}_3^-$) and phosphates (${PO}_4^{3-}$), into a water body. These nutrients, often from agricultural runoff or sewage, stimulate the dense growth of plant life (algal blooms). The subsequent decomposition of this excess biomass by aerobic bacteria depletes the dissolved oxygen (${DO}$), leading to the death of fish and other aquatic life.
21. What is the single largest anthropogenic source of Carbon Monoxide (${CO}$) and unburnt hydrocarbons in the atmosphere of metropolitan cities?
ⓐ. Thermal power plants
ⓑ. Volcanic eruptions
ⓒ. Industrial solvent use
ⓓ. Automobile exhaust
Correct Answer: Automobile exhaust
Explanation: In urban areas, the incomplete combustion of gasoline and diesel in automobile engines is the largest contributor to ${Carbon Monoxide (CO)}$ and unburnt hydrocarbon pollution. ${CO}$ is a toxic gas that blocks the transport of oxygen by blood. Unburnt hydrocarbons contribute to the formation of photochemical smog. Thermal power plants are primarily major sources of ${SO}_2$ and particulate matter.
22. The discharge of untreated wastewater containing toxic heavy metals like Cadmium, Lead, and Mercury into rivers and streams primarily originates from which major source?
ⓐ. Electroplating and metallurgical industries
ⓑ. Domestic sewage treatment plants
ⓒ. Agricultural runoff
ⓓ. Natural weathering of rocks
Correct Answer: Electroplating and metallurgical industries
Explanation: Heavy metals are crucial in many industrial processes, particularly electroplating, dyeing, chemical manufacturing, and metallurgical operations. When industrial effluent is discharged without proper treatment, these toxic, non-biodegradable metals pollute water sources. Domestic sewage contributes organic load (${BOD}$), and agricultural runoff contributes nutrients (Nitrates/Phosphates).
23. Eutrophication, the condition of oxygen depletion in water bodies, is mainly initiated by the runoff of excess plant nutrients. The primary source of these Nitrates (${NO}_3^-$) and Phosphates (${PO}_4^{3-}$) is:
ⓐ. Direct discharge of industrial cooling water
ⓑ. Exhaust from jet aircraft
ⓒ. Fertilizers used in agriculture
ⓓ. Ash generated by incinerators
Correct Answer: Fertilizers used in agriculture
Explanation: Modern agriculture relies heavily on nitrogenous and phosphatic fertilizers to boost crop yields. When rainwater or irrigation washes the surplus, unused fertilizer from the fields into nearby water bodies, the influx of these nutrients causes rapid, excessive growth of algae (algal bloom), leading directly to eutrophication.
24. In countries that rely on coal for electricity generation, the most abundant gaseous pollutant released from thermal power plants that contributes to atmospheric pollution is:
ⓐ. Sulphur Dioxide (${SO}_2$)
ⓑ. Methane (${CH}_4$)
ⓒ. Carbon Monoxide (${CO}$)
ⓓ. Chlorofluorocarbons (CFCs)
Correct Answer: Sulphur Dioxide (${SO}_2$)
Explanation: Coal, especially low-grade coal, contains significant amounts of sulphur. When coal is burned in thermal power plants, the sulphur is oxidized, releasing large quantities of Sulphur Dioxide (${SO}_2$) into the atmosphere. ${SO}_2$ is a respiratory irritant and a primary precursor to acid rain (${H}_2{SO}_4$). ${CO}$ and ${CH}_4$ are mainly associated with automobiles and landfills/agriculture, respectively.
25. The most significant source contributing to the high Biochemical Oxygen Demand (BOD) levels in river water is:
ⓐ. Treated industrial effluents
ⓑ. Thermal discharge from nuclear power plants
ⓒ. Untreated domestic sewage and animal waste
ⓓ. Acid mine drainage
Correct Answer: Untreated domestic sewage and animal waste
Explanation: BOD is a measure of the amount of dissolved oxygen required by aerobic microorganisms to decompose the organic matter present in a water sample. Domestic sewage is rich in highly decomposable organic waste (food scraps, human waste). The decomposition of this large organic load consumes vast amounts of dissolved oxygen, hence causing the ${BOD}$ level to rise significantly, often resulting in an anaerobic environment that kills aquatic life.
26. Which of the following human activities was the primary source that led to the widespread release of Chlorofluorocarbons (CFCs) into the atmosphere, causing ozone layer depletion?
ⓐ. The burning of gasoline in automobiles.
ⓑ. Use as refrigerants and aerosol propellants.
ⓒ. The manufacturing of plastics and polymers.
ⓓ. High-altitude flight operations.
Correct Answer: Use as refrigerants and aerosol propellants.
Explanation: CFCs were widely adopted due to their stability and non-flammability. Their major industrial uses included coolants in refrigerators and air conditioners (refrigerants), as foam blowing agents, and as pressurized propellants in aerosol cans. Their release during manufacture and disposal allowed them to reach the stratosphere, where they initiated the catalytic destruction of the ozone layer.
27. The increase in the temperature of a water body, often leading to a reduction in its dissolved oxygen content, known as thermal pollution, is predominantly caused by the discharge of:
ⓐ. Highly acidic wastewater from chemical factories.
ⓑ. Heated rainwater runoff from urban concrete surfaces.
ⓒ. Water contaminated with radioactive fallout.
ⓓ. Waste hot water from power plant cooling systems.
Correct Answer: Waste hot water from power plant cooling systems.
Explanation: Thermal power plants and nuclear power plants use vast amounts of water from lakes or rivers as a coolant to condense steam. This heated water is then discharged back into the original source at a much higher temperature. This sudden increase in water temperature reduces the solubility of oxygen in the water and stresses aquatic organisms, defining thermal pollution.
28. In agricultural practices, the application of which group of chemicals is a major source of persistent soil and water pollution due to their highly stable, non-biodegradable nature?
ⓐ. Organochlorine pesticides (e.g., DDT, Aldrin)
ⓑ. Urea and Ammonium Sulphate (nitrogen fertilizers)
ⓒ. Potassium Chloride (potash fertilizers)
ⓓ. Common herbicides like glyphosate
Correct Answer: Organochlorine pesticides (e.g., DDT, Aldrin)
Explanation: Organochlorine pesticides are highly effective against pests but are non-biodegradable and fat-soluble. They persist in the soil and water for decades, eventually entering the food chain and causing biomagnification. While other options (B, C, D) cause environmental issues (like eutrophication or toxicity), the persistent nature of organochlorines makes them a key source of long-term soil and water pollution.
29. To combat pollution from automobile exhaust, vehicles are equipped with catalytic converters. These devices primarily work by facilitating what type of chemical reaction on the harmful gaseous emissions?
ⓐ. Photochemical dissociation
ⓑ. Oxidation and Reduction (Redox) reactions
ⓒ. Acid-base neutralization reactions
ⓓ. Simple physical filtration
Correct Answer: Oxidation and Reduction (Redox) reactions
Explanation: Catalytic converters use precious metals (like Platinum, Palladium, Rhodium) as catalysts to facilitate redox reactions. They oxidize unburnt hydrocarbons and ${CO}$ into ${CO}_2$ and ${H}_2{O}$ (oxidation), and they reduce nitrogen oxides (${NO}_{{x}}$) into harmless ${N}_2$ gas (reduction), thereby significantly lowering the toxicity of the exhaust gases before they are released.
30. The accumulation of which highly toxic heavy metal in rice paddies, often originating from mine waste and smelting activities, is responsible for the painful Itai-Itai disease (Ouch-Ouch disease)?
ⓐ. Mercury (${Hg}$)
ⓑ. Lead (${Pb}$)
ⓒ. Cadmium (${Cd}$)
ⓓ. Arsenic (${As}$)
Correct Answer: Cadmium (${Cd}$)
Explanation: The Itai-Itai disease, first documented in Japan, is a classic example of severe environmental pollution leading to human tragedy. It was caused by chronic Cadmium (${Cd}$) poisoning. The ${Cd}$ was released into the Jinzu River from nearby mining and smelting operations and accumulated in the rice grown in the irrigated paddies, leading to brittle bones and kidney failure in the local population who consumed the rice. Mercury causes Minamata disease.
31. Which of the following is the primary chemical characteristic of Classical Smog (also known as reducing smog or London Smog)?
ⓐ. It is dominated by photochemical oxidants like ozone and ${PAN}$.
ⓑ. It consists mainly of ${SO}_2$, smoke, and fog.
ⓒ. It occurs mostly during the summer in dry, sunny conditions.
ⓓ. It is caused by the reaction of hydrocarbons and nitrogen oxides.
Correct Answer: It consists mainly of ${SO}_2$, smoke, and fog.
Explanation: Classical Smog is a mixture of smoke, fog, and sulphur dioxide (${SO}_2$). It is historically associated with coal burning and is known as reducing smog because of the chemical nature of ${SO}_2$. It typically occurs in cool, humid, and cloudy conditions (like the London Great Smog of 1952). Photochemical Smog (Options A, C, D) is dominated by ozone and requires sunlight.
32. The characteristic brownish haze or yellowish-brown colour often observed in photochemical smog is primarily due to the presence of which gas?
ⓐ. Sulphur Dioxide (${SO}_2$)
ⓑ. Tropospheric Ozone (${O}_3$)
ⓒ. Carbon Monoxide (${CO}$)
ⓓ. Nitrogen Dioxide (${NO}_2$)
Correct Answer: Nitrogen Dioxide (${NO}_2$)
Explanation: Nitrogen Dioxide (${NO}_2$) is the only pollutant gas among the common atmospheric pollutants that is strongly coloured (reddish-brown). It is a key primary and secondary pollutant in photochemical smog. The photochemical reactions start with the photodissociation of ${NO}_2$ in the presence of sunlight: ${NO}_2({g}) \xrightarrow{h\nu} {NO}({g}) + {O}({g})$. The remaining brownish haze is visible ${NO}_2$.
33. Acid rain is defined as precipitation with a ${pH}$ value less than:
ⓐ. $5.6$
ⓑ. $7.0$
ⓒ. $6.5$
ⓓ. $4.5$
Correct Answer: $5.6$
Explanation: Normal rainwater is naturally slightly acidic, with a ${pH}$ of about $5.6$. This natural acidity results from the dissolution of atmospheric carbon dioxide (${CO}_2$) to form weak carbonic acid (${H}_2{CO}_3$):
$${CO}_2({g}) + {H}_2{O}({l}) \rightleftharpoons {H}_2{CO}_3({aq})$$
Rainfall with a ${pH}$ value less than $5.6$ is officially defined as acid rain, resulting primarily from the presence of strong acids like ${H}_2{SO}_4$ and ${HNO}_3$ formed from ${SO}_2$ and ${NO}_{{x}}$ pollutants.
34. Carbon Monoxide (${CO}$) is a dangerous air pollutant because of its high affinity for the blood component that carries oxygen. ${CO}$ poisoning occurs because it binds to which molecule much more strongly than oxygen?
ⓐ. Haemoglobin
ⓑ. Myoglobin
ⓒ. Plasma
ⓓ. Cytochrome C oxidase
Correct Answer: Haemoglobin
Explanation: Carbon Monoxide is highly toxic because it binds irreversibly with haemoglobin (Hb) in the blood to form a stable compound called carboxyhaemoglobin (${COHb}$). The affinity of ${CO}$ for ${Hb}$ is about 200-300 times greater than that of oxygen. This drastically reduces the oxygen-carrying capacity of the blood, leading to asphyxiation and, eventually, death, even at low ${CO}$ concentrations.
35. The formation of harmful ground-level ozone (${O}_3$) in the troposphere requires the presence of which three key components?
ⓐ. ${CO}_2$, ${H}_2{O}$, and Sunlight
ⓑ. ${SO}_2$, Smoke, and ${NO}_{{x}}$
ⓒ. ${NO}_{{x}}$, Volatile Organic Compounds (VOCs), and Sunlight
ⓓ. ${CFCs}$, Oxygen, and Low Temperatures
Correct Answer: ${NO}_{{x}}$, Volatile Organic Compounds (VOCs), and Sunlight
Explanation: Tropospheric ozone is a secondary pollutant formed during photochemical smog. It requires three ingredients: Nitrogen Oxides (${NO}_{{x}}$), Volatile Organic Compounds (VOCs) (which are unburnt hydrocarbons), and a source of energy, Sunlight. The UV radiation triggers the reaction sequence where ${NO}_2$ dissociates, releasing atomic oxygen (${O}$), which then combines with molecular oxygen (${O}_2$) to form ${O}_3$.
36. Particulate Matter (PM) is classified based on its aerodynamic diameter. Which size category of ${PM}$ poses the greatest risk to human health, as it can penetrate deep into the lungs and potentially enter the bloodstream?
ⓐ. ${PM}_{10}$ (particles less than $10$ $\mu{m}$ in diameter)
ⓑ. ${PM}_{2.5}$ (particles less than $2.5$ $\mu{m}$ in diameter)
ⓒ. ${PM}_{1.0}$ (particles less than $1.0$ $\mu{m}$ in diameter)
ⓓ. ${PM}_{50}$ (particles less than $50$ $\mu{m}$ in diameter)
Correct Answer: ${PM}_{2.5}$ (particles less than $2.5$ $\mu{m}$ in diameter)
Explanation: Particles are categorized by size. ${PM}_{10}$ can enter the respiratory tract, but ${PM}_{2.5}$ (fine particulates) are small enough to reach the gas-exchange regions of the lungs (alveoli) and cause severe respiratory and cardiovascular problems. They are often generated by combustion sources like vehicles and power plants.
37. The overall chemical equation representing the formation of the strong acid ${Nitric Acid}$ (${HNO}_3$) from Nitrogen Dioxide (${NO}_2$) in the atmosphere is:
ⓐ. ${NO}_2 + {H}_2{O} \rightarrow {HNO}_3 + {H}_2$
ⓑ. ${NO}_2 + {O}_2 \rightarrow {NO}_3$
ⓒ. $2{NO}_2 + 2{O}_2 + {H}_2{O} \rightarrow 2{HNO}_3 + {O}$
ⓓ. $4{NO}_2({g}) + 2{H}_2{O}({l}) + {O}_2({g}) \rightarrow 4{HNO}_3({aq})$
Correct Answer: $4{NO}_2({g}) + 2{H}_2{O}({l}) + {O}_2({g}) \rightarrow 4{HNO}_3({aq})$
Explanation: Nitrogen dioxide (${NO}_2$), a primary pollutant, is oxidized in the atmosphere and reacts with moisture to form Nitric Acid (${HNO}_3$), one of the two main components of acid rain (the other being ${H}_2{SO}_4$). The balanced equation shows the reaction of ${NO}_2$ with water and atmospheric oxygen (${O}_2$) to yield ${HNO}_3$. This acid is highly corrosive and contributes significantly to the harmful effects of acid rain.
38. Photochemical smog is most likely to occur in geographical areas characterized by:
ⓐ. High temperatures and intense solar radiation.
ⓑ. Low temperatures and high humidity with coal burning.
ⓒ. Coastal areas with high salinity.
ⓓ. High rainfall and forested areas.
Correct Answer: High temperatures and intense solar radiation.
Explanation: Photochemical smog (Los Angeles smog) is a complex mixture of pollutants formed when sunlight acts on emissions like ${NO}_{{x}}$ and ${VOCs}$. The formation process is highly dependent on light intensity and temperature, as the chemical reactions speed up considerably in warm, sunny conditions. Option B describes the conditions for Classical (London) Smog.
39. The primary visible effect of Sulphur Dioxide (${SO}_2$) on plant life is:
ⓐ. Inhibition of seed germination.
ⓑ. Excessive elongation of the stem.
ⓒ. Chlorosis (yellowing of leaves) and Necrosis (dead areas).
ⓓ. Increase in the rate of photosynthesis.
Correct Answer: Chlorosis (yellowing of leaves) and Necrosis (dead areas).
Explanation: ${SO}_2$ is highly phytotoxic. When ${SO}_2$ gas enters plant leaves through stomata, it dissolves and forms sulphurous acid, disrupting cellular functions. This damage leads to chlorosis (yellowing due to chlorophyll destruction) and necrosis (the premature death of tissues, forming dead spots on the leaves), which severely affects the plant’s ability to photosynthesize.
40. Which of the following particulate pollutants is best categorized as a liquid aerosol?
ⓐ. Soot from diesel engines
ⓑ. Fly ash from thermal power plants
ⓒ. Mist from herbicide/pesticide sprays
ⓓ. Dust from cement manufacturing
Correct Answer: Mist from herbicide/pesticide sprays
Explanation: Aerosols are solid particles or liquid droplets suspended in the air. Mist specifically refers to liquid droplets formed by condensation or by atomizing a liquid (like spray nozzles for pesticides, herbicides, or acid mist from industrial processes). Soot, fly ash, and cement dust are examples of solid particulate matter.
41. Which of the following is the defining characteristic of Photochemical Smog?
ⓐ. It is highly oxidizing in nature due to the presence of ${O}_3$ and ${PAN}$.
ⓑ. It is a reducing smog caused primarily by ${SO}_2$ and smoke.
ⓒ. It occurs mainly in cold, humid climates due to coal burning.
ⓓ. It is formed only in the presence of water vapor and dust particles.
Correct Answer: It is highly oxidizing in nature due to the presence of ${O}_3$ and ${PAN}$.
Explanation: Photochemical smog is also known as oxidizing smog because its major components, such as tropospheric ozone (${O}_3$) and peroxyacetyl nitrates (${PAN}$), are powerful oxidizing agents. Unlike Classical Smog (which is reducing and dominated by ${SO}_2$), photochemical smog occurs in warm, dry, and sunny conditions, where these oxidizers are formed through sunlight-driven chemical reactions involving ${NO}_{{x}}$ and hydrocarbons.
42. Photochemical smog is a mixture of several chemical species. Which compound among the following is a product of the reaction between unburnt hydrocarbons and ${NO}_{{x}}$ in the presence of sunlight, making it a key component and a lachrymator (tear gas)?
ⓐ. Sulphur Trioxide (${SO}_3$)
ⓑ. Peroxyacetyl Nitrate (${PAN}$)
ⓒ. Carbon Monoxide (${CO}$)
ⓓ. Nitrous Oxide (${N}_2{O}$)
Correct Answer: Peroxyacetyl Nitrate (${PAN}$)
Explanation: Peroxyacetyl Nitrate (${PAN}$) is a highly reactive secondary pollutant unique to photochemical smog. It is formed via complex free-radical reactions involving hydrocarbons (or Volatile Organic Compounds, ${VOCs}$), ${NO}_{{x}}$, and molecular oxygen. ${PAN}$ is a powerful plant toxin and a strong eye irritant (lachrymator) that contributes significantly to the harmful effects of smog.
43. The formation of ground-level ozone (${O}_3$) in photochemical smog is initiated by the absorption of sunlight by a primary pollutant. The first step involves the photodissociation of:
ⓐ. Tropospheric Ozone (${O}_3$)
ⓑ. Carbon Monoxide (${CO}$)
ⓒ. Nitrogen Dioxide (${NO}_2$)
ⓓ. Hydrocarbons (${RH}$)
Correct Answer: Nitrogen Dioxide (${NO}_2$)
Explanation: The chemical cycle begins when Nitrogen Dioxide (${NO}_2$) absorbs sunlight ($h\nu$) and undergoes photodissociation to yield Nitric Oxide (${NO}$) and a free oxygen atom (${O}$):
$${NO}_2({g}) \xrightarrow{h\nu} {NO}({g}) + {O}({g})$$
The resulting highly reactive atomic oxygen (${O}$) then combines with molecular oxygen (${O}_2$) to form ozone (${O}_3$): ${O}({g}) + {O}_2({g}) \rightleftharpoons {O}_3({g})$.
44. Which major component of photochemical smog is responsible for causing the “silvering” or “glazing” (bronzing) of the lower surface of green leaves, severely impacting agriculture?
ⓐ. ${Nitrogen Dioxide}$ (${NO}_2$)
ⓑ. ${Peroxyacetyl Nitrate}$ (${PAN}$)
ⓒ. Aldehydes (e.g., Formaldehyde)
ⓓ. Ozone (${O}_3$)
Correct Answer: Ozone (${O}_3$)
Explanation: Tropospheric Ozone (${O}_3$) is an extremely strong oxidizing agent and is considered the most phytotoxic (toxic to plants) component of photochemical smog. It causes visible injury to leaves, often resulting in bronzing or stippling on the upper surfaces and growth retardation, leading to significant crop damage. ${PAN}$ is also phytotoxic, but ${O}_3$ is generally the more damaging component.
45. The complete chemical formula for Peroxyacetyl Nitrate (PAN), a key secondary pollutant in photochemical smog, is:
ⓐ. ${CH}_3{CO}{O}_2{N}$
ⓑ. ${CH}_3{ONO}_2$
ⓒ. ${C}_2{H}_5{NO}_3$
ⓓ. ${CH}_3{COO}{NO}_2$
Correct Answer: ${CH}_3{COO}{NO}_2$
Explanation: Peroxyacetyl Nitrate (${PAN}$) is the acetyl radical (${CH}_3{CO}$) attached to a peroxy nitrate group (${O}_2{NO}_2$). The correct formula is ${CH}_3{COO}{NO}_2$, which clearly shows the acetyl group, the peroxy bridge, and the nitrate group. Its formation is indicative of intense photochemical activity.
46. Which atmospheric condition, apart from the presence of ${NO}_{{x}}$ and ${VOCs}$, is absolutely essential for the formation of significant concentrations of photochemical smog?
ⓐ. High velocity winds for pollutant dispersal.
ⓑ. A thermal inversion layer over the area.
ⓒ. High humidity and cold temperature.
ⓓ. The presence of atmospheric ${SO}_2$ (Sulphur Dioxide).
Correct Answer: A thermal inversion layer over the area.
Explanation: Thermal Inversion is a meteorological phenomenon where a layer of warm air sits above a layer of cooler air near the ground. This stable condition prevents the normal vertical mixing and dispersal of pollutants, trapping the ${NO}_{{x}}$ and ${VOCs}$ close to the surface. This high concentration, combined with sunlight, allows for maximum photochemical reaction rates, leading to severe smog episodes.
47. The primary health effect of acute exposure to high concentrations of Ozone (${O}_3$) in photochemical smog on humans is:
ⓐ. Irritation of the respiratory system, including cough and chest pain.
ⓑ. Binding to haemoglobin, causing asphyxiation.
ⓒ. Severe kidney and liver damage.
ⓓ. Permanent damage to bone structure.
Correct Answer: Irritation of the respiratory system, including cough and chest pain.
Explanation: ${Ozone}$ is a powerful oxidizing agent. When inhaled, it reacts with biological tissues, particularly in the respiratory tract. Acute exposure causes inflammation, leading to coughing, throat irritation, chest pain, and difficulty breathing, especially for people with asthma or other respiratory conditions. Binding to haemoglobin is characteristic of Carbon Monoxide (${CO}$) poisoning.
48. The removal of Nitric Oxide (${NO}$) from the atmosphere in the smog cycle occurs when it reacts with ozone. The balanced chemical equation for this removal step is:
ⓐ. $2{NO} + {O}_2 \rightarrow 2{NO}_2$
ⓑ. ${NO} + {O}_3 \rightarrow {NO}_2 + {O}_2$
ⓒ. ${NO} + {H}_2{O} \rightarrow {HNO}_2 + {H}$
ⓓ. ${NO} + {CO} \rightarrow {N} + {CO}_2$
Correct Answer: ${NO} + {O}_3 \rightarrow {NO}_2 + {O}_2$
Explanation: In the cycle, the ${O}_3$ formed during the day reacts with Nitric Oxide (${NO}$) to regenerate ${NO}_2$ and ${O}_2$. This reaction prevents the excessive build-up of ${O}_3$ in the absence of other hydrocarbons. However, when ${VOCs}$ are present, they react with ${NO}$, preventing this ${O}_3$ scavenging reaction, allowing ${O}_3$ concentration to rise significantly.
49. Which of the following is an effective strategy to reduce the formation of photochemical smog in a heavily polluted urban area?
ⓐ. Encouraging the burning of coal instead of petroleum products.
ⓑ. Increasing the discharge of industrial ${SO}_2$ to neutralize ${NO}_{{x}}$.
ⓒ. Installing catalytic converters in vehicles to reduce ${NO}_{{x}}$ and hydrocarbon emissions.
ⓓ. Introducing ${CFCs}$ into the atmosphere to block UV radiation.
Correct Answer: Installing catalytic converters in vehicles to reduce ${NO}_{{x}}$ and hydrocarbon emissions.
Explanation: Photochemical smog formation is directly dependent on the presence of its precursors: ${NO}_{{x}}$ and ${VOCs}$. Catalytic converters are designed to reduce these emissions by converting ${NO}_{{x}}$ back into ${N}_2$ and ${O}_2$, and oxidizing ${VOCs}$ into ${CO}_2$ and ${H}_2{O}$. This reduction in precursor concentration is the most direct and effective strategy to mitigate photochemical smog.
50. The term Volatile Organic Compounds (VOCs) in the context of smog formation typically refers to:
ⓐ. Stable, non-reactive gaseous hydrocarbons.
ⓑ. Compounds containing only Carbon, Oxygen, and Nitrogen.
ⓒ. Fluorinated gases used in industrial processes.
ⓓ. Unburnt or partially combusted hydrocarbons and organic solvents.
Correct Answer: Unburnt or partially combusted hydrocarbons and organic solvents.
Explanation: VOCs are organic chemicals that have a high vapour pressure at ordinary room temperature, meaning they easily evaporate (volatilize). In smog chemistry, this primarily refers to unburnt fuel (${C}_8{H}_{18}$, etc.) from vehicle exhaust, gasoline vapour, and evaporated organic solvents from industries (e.g., paints, printing). These ${VOCs}$ are highly reactive and participate in the free-radical reactions that form ${O}_3$ and ${PAN}$.
51. Classical smog is also often referred to as Reducing Smog because of the chemical nature of its primary gaseous component. Which gas gives it this reducing character?
ⓐ. Nitrogen Dioxide (${NO}_2$)
ⓑ. Tropospheric Ozone (${O}_3$)
ⓒ. Carbon Monoxide (${CO}$)
ⓓ. Sulphur Dioxide (${SO}_2$)
Correct Answer: Sulphur Dioxide (${SO}_2$)
Explanation: Classical Smog, historically prevalent in London, is dominated by Sulphur Dioxide (${SO}_2$) and particulate matter (smoke). Since ${SO}_2$ readily undergoes oxidation to form ${SO}_3$ and ${H}_2{SO}_4$, it acts as a reducing agent in many atmospheric reactions. Therefore, this smog mixture as a whole is classified as reducing smog, in contrast to photochemical smog which is oxidizing.
52. Classical Smog episodes, like the Great Smog of London in 1952, typically occur under which combination of climatic conditions?
ⓐ. High temperature and low humidity with intense sunlight.
ⓑ. Cool, humid, and cloudy weather with a high concentration of coal smoke.
ⓒ. Tropical regions with heavy rainfall and strong winds.
ⓓ. High altitude, dry air, and frequent thermal inversions.
Correct Answer: Cool, humid, and cloudy weather with a high concentration of coal smoke.
Explanation: Classical smog is formed when combustion products, primarily from burning coal, are trapped near the ground. This trapping is maximized in cool, damp conditions often associated with a temperature inversion. The smoke, fog (high humidity), and ${SO}_2$ mix near the surface, forming a dense, noxious blanket. Option A describes the conditions for Photochemical Smog.
53. The primary particulate matter component that distinguishes Classical Smog from Photochemical Smog is:
ⓐ. Peroxyacetyl Nitrate (${PAN}$)
ⓑ. Acid Mist (${H}_2{SO}_4$ liquid aerosol)
ⓒ. Soot/Smoke from coal combustion
ⓓ. ${NO}_{{x}}$ compounds
Correct Answer: Soot/Smoke from coal combustion
Explanation: Classical Smog is a mixture of ${SO}_2$, fog, and smoke particles, which are solid carbonaceous material (soot) from the incomplete burning of coal and other fossil fuels. These particulates serve as condensation nuclei for water vapour and reaction surfaces for ${SO}_2$ oxidation. While acid mist forms within classical smog, the initial differentiating ingredient is the heavy load of coal smoke.
54. The process by which Sulphur Dioxide (${SO}_2$) in Classical Smog is converted into the major acid component (${H}_2{SO}_4$) involves an intermediate step where ${SO}_2$ is first converted to:
ⓐ. Sulphur Trioxide (${SO}_3$)
ⓑ. Sulphurous Acid (${H}_2{SO}_3$)
ⓒ. Sulphuric Acid (${H}_2{SO}_4$)
ⓓ. Hydrogen Sulphide (${H}_2{S}$)
Correct Answer: Sulphur Trioxide (${SO}_3$)
Explanation: The oxidation of ${SO}_2$ is a key reaction. ${SO}_2$ reacts with oxygen (${O}_2$) in the air, often catalyzed by particulate matter or metal ions, to form Sulphur Trioxide (${SO}_3$):
$$2{SO}_2({g}) + {O}_2({g}) \xrightarrow{{Catalyst}} 2{SO}_3({g})$$
The ${SO}_3$ then rapidly reacts with water vapor (${H}_2{O}$) to produce highly corrosive Sulphuric Acid (${H}_2{SO}_4$), a major component of acid mist and acid rain.
55. How does the presence of fog (high humidity) enhance the formation and severity of Classical Smog?
ⓐ. Fog absorbs ${NO}_{{x}}$, accelerating the photochemical reaction.
ⓑ. Fog acts as a cooling agent, preventing pollutants from rising.
ⓒ. Fog causes the degradation of soot particles into harmless ${CO}_2$.
ⓓ. Water droplets dissolve ${SO}_2$ and catalyze its oxidation to form acid mist.
Correct Answer: Water droplets dissolve ${SO}_2$ and catalyze its oxidation to form acid mist.
Explanation: In high humidity, the water droplets in the fog act as micro-reactors. ${SO}_2$ gas dissolves readily in water to form sulphurous acid (${H}_2{SO}_3$), which is then easily oxidized to form the strong Sulphuric Acid (${H}_2{SO}_4$) within the droplets. This creates a dense, acidic mist that is highly irritating and damaging.
56. The most severe human health effect associated with acute exposure to Classical Smog is:
ⓐ. Skin cancer due to UV radiation.
ⓑ. Acute respiratory failure and bronchitis, particularly in the elderly and infirm.
ⓒ. Neurological damage due to heavy metals.
ⓓ. Eye irritation due to ${PAN}$.
Correct Answer: Acute respiratory failure and bronchitis, particularly in the elderly and infirm.
Explanation: The combination of high concentrations of ${SO}_2$ (a strong irritant) and tiny, deeply penetrative ${PM}$ (soot/smoke) characterizes classical smog. ${SO}_2$ can cause bronchoconstriction and inflammation. The Great Smog incident demonstrated that this combination led to thousands of premature deaths, primarily from bronchitis, pneumonia, and acute respiratory illnesses.
57. A major difference between Classical Smog and Photochemical Smog in terms of the main source of precursors is:
ⓐ. Classical smog precursors come only from natural sources, while photochemical smog precursors are man-made.
ⓑ. Photochemical smog involves primary pollutants from stationary sources, while classical smog involves mobile sources.
ⓒ. Classical smog precursors (${SO}_2$, smoke) are primarily from burning coal/fuel oil for heat and power.
ⓓ. Photochemical smog involves only solid particulates, while classical smog involves only gases.
Correct Answer: Classical smog precursors (${SO}_2$, smoke) are primarily from burning coal/fuel oil for heat and power.
Explanation: Historically, Classical Smog was caused by massive emissions from burning high-sulphur coal for industrial and residential heating. Precursors for Photochemical Smog (${NO}_{{x}}$, ${VOCs}$) are predominantly sourced from automobile exhaust (mobile sources) and unevaporated organic solvents, rather than stationary coal burning.
58. Which of the following is a key chemical reaction that contributes to the adverse effects of Classical Smog on materials like limestone or marble statues?
ⓐ. ${CaCO}_3 + {H}_2{O} \rightarrow {Ca}({OH})_2 + {CO}_2$
ⓑ. ${NO} + {O}_3 \rightarrow {NO}_2 + {O}_2$
ⓒ. ${C} + {O}_2 \rightarrow {CO}_2$
ⓓ. ${CaCO}_3({s}) + {H}_2{SO}_4({aq}) \rightarrow {CaSO}_4({s}) + {H}_2{O}({l}) + {CO}_2({g})$
Correct Answer: ${CaCO}_3({s}) + {H}_2{SO}_4({aq}) \rightarrow {CaSO}_4({s}) + {H}_2{O}({l}) + {CO}_2({g})$
Explanation: The Sulphuric Acid (${H}_2{SO}_4$) component of Classical Smog and acid rain is highly corrosive. Limestone and marble are chemically Calcium Carbonate (${CaCO}_3$). The strong acid reacts with the marble to form Calcium Sulphate (${CaSO}_4$) which is water-soluble and easily washed away or causes the surface to flake, leading to the decay of buildings and monuments.
59. If the concentration of ${SO}_2$ in the atmosphere is measured at $10{ ppm}$ (parts per million) during a smog event, and a sample of $1{ L}$ of air is collected at ${STP}$, the approximate volume of ${SO}_2$ present is:
ⓐ. $10{ mL}$
ⓑ. $1.0{ mL}$
ⓒ. $0.01{ mL}$
ⓓ. $0.001{ mL}$
Correct Answer: $0.01{ mL}$
Explanation: The concentration of a gaseous pollutant in ${ppm}$ (parts per million) by volume is calculated as:
$${ppm} = \dfrac{{Volume of Pollutant}}{{Volume of Air}} \times 10^6$$
Given ${ppm} = 10$ and Volume of Air $= 1{ L} = 1000{ mL}$. Let ${V}_{{SO}_2}$ be the volume of ${SO}_2$.
$$10 = \dfrac{{V}_{{SO}_2}}{1000{ mL}} \times 1,000,000$$
$${V}_{{SO}_2} = \dfrac{10 \times 1000}{1,000,000} = \dfrac{10,000}{1,000,000} = 0.01{ mL}$$
60. The decomposition of pollutants in Classical Smog, such as the oxidation of ${SO}_2$ to ${SO}_3$, is highly dependent on which factor in the presence of ${PM}$ (particulate matter)?
ⓐ. The catalytic surface area provided by soot particles
ⓑ. High concentration of ozone
ⓒ. Intense UV radiation
ⓓ. High vapor pressure of ${SO}_2$
Correct Answer: The catalytic surface area provided by soot particles
Explanation: Unlike photochemical smog which is driven by sunlight (UV radiation and ${O}_3$), the key accelerator for the ${SO}_2$ oxidation in Classical Smog is the presence of fine particulate matter (soot). These solid particles provide an enormous surface area on which the ${SO}_2$ and ${O}_2$ molecules can adsorb and react, effectively acting as heterogeneous catalysts for the conversion to ${SO}_3$ and subsequently to ${H}_2{SO}_4$.
61. The two primary gaseous pollutants responsible for the formation of acid rain are:
ⓐ. Sulphur Dioxide (${SO}_2$) and Nitrogen Oxides (${NO}_{{x}}$).
ⓑ. Carbon Dioxide (${CO}_2$) and Methane (${CH}_4$).
ⓒ. Carbon Monoxide (${CO}$) and Tropospheric Ozone (${O}_3$).
ⓓ. Chlorofluorocarbons (${CFCs}$) and ${Hydrocarbons}$.
Correct Answer: Sulphur Dioxide (${SO}_2$) and Nitrogen Oxides (${NO}_{{x}}$).
Explanation: Acid rain is primarily caused by the emission of ${SO}_2$ (from burning coal/fuel oil) and ${NO}_{{x}}$ (from vehicle exhaust and power plants). These gases react with atmospheric water vapor and oxygen to form strong mineral acids: Sulphuric Acid (${H}_2{SO}_4$) and Nitric Acid (${HNO}_3$). ${CO}_2$ causes the natural slight acidity of rain (${pH} \approx 5.6$), but ${SO}_2$ and ${NO}_{{x}}$ are responsible for the severe, damaging acidity.
62. The final step in the formation of Sulphuric Acid (${H}_2{SO}_4$) in the atmosphere involves the reaction of Sulphur Trioxide (${SO}_3$) with water (${H}_2{O}$). Which statement accurately describes the chemical nature of this final product in acid rain?
ⓐ. ${H}_2{SO}_4$ is a weak acid that barely dissociates in water.
ⓑ. ${H}_2{SO}_4$ acts as a greenhouse gas, trapping heat.
ⓒ. ${H}_2{SO}_4$ is a strong acid that ionizes almost completely in water.
ⓓ. ${H}_2{SO}_4$ is a secondary pollutant that causes ozone depletion.
Correct Answer: ${H}_2{SO}_4$ is a strong acid that ionizes almost completely in water.
Explanation: Sulphuric Acid (${H}_2{SO}_4$) is one of the strongest common mineral acids. Its strong acidic nature means it dissociates nearly $100\\%$ in water, releasing a high concentration of ${H}^{+}$ ions. This high concentration of ions is the reason for the highly corrosive nature and low ${pH}$ (typically $4.0$ to $4.5$) of acid rain, causing widespread environmental damage.
63. Acid rain is defined as precipitation having a ${pH}$ value lower than the natural ${pH}$ of rain, which is:
ⓐ. $7.0$ (Neutral ${pH}$).
ⓑ. $5.6$ (Natural ${pH}$ of rain).
ⓒ. $4.5$ (Typical value of severe acid rain).
ⓓ. $3.0$ (Extremely acidic value).
Correct Answer: $5.6$ (Natural ${pH}$ of rain).
Explanation: Pure water has a neutral ${pH}$ of $7.0$. However, natural rainwater is slightly acidic because it dissolves atmospheric carbon dioxide (${CO}_2$) to form weak carbonic acid (${H}_2{CO}_3$). This equilibrium lowers the ${pH}$ to approximately $5.6$. Precipitation with a ${pH}$ value below $5.6$ is officially classified as acid rain because the excess acidity must be due to the presence of strong acids (${H}_2{SO}_4$ and ${HNO}_3$).
64. Acid rain causes severe damage to historical monuments and buildings made of marble (${CaCO}_3$). This decay process is chemically represented by the reaction:
ⓐ. ${CaCO}_3 + 2{HNO}_3 \rightarrow {Ca}({NO}_3)_2 + {H}_2{CO}_3$
ⓑ. ${CaCO}_3 + {CO}_2 + {H}_2{O} \rightarrow {Ca}({HCO}_3)_2$
ⓒ. ${CaCO}_3({s}) + 2{HCl}({aq}) \rightarrow {CaCl}_2({aq}) + {H}_2{O}({l}) + {CO}_2({g})$
ⓓ. ${CaCO}_3({s}) + {H}_2{SO}_4({aq}) \rightarrow {CaSO}_4({s}) + {H}_2{O}({l}) + {CO}_2({g})$
Correct Answer: ${CaCO}_3({s}) + {H}_2{SO}_4({aq}) \rightarrow {CaSO}_4({s}) + {H}_2{O}({l}) + {CO}_2({g})$
Explanation: Marble is Calcium Carbonate (${CaCO}_3$). The strong Sulphuric Acid (${H}_2{SO}_4$), a major component of acid rain, reacts with the marble to form Calcium Sulphate (${CaSO}_4$). ${CaSO}_4$ is more porous and partially water-soluble (plaster of Paris), causing the marble surface to crumble, flake off, or be easily washed away, a process sometimes called ‘stone leprosy’.
65. In the atmosphere, Nitrogen Dioxide (${NO}_2$) reacts with water and oxygen to form Nitric Acid (${HNO}_3$), a key acid rain component. The balanced overall equation for this process is:
ⓐ. $2{NO}_2 + {H}_2{O} \rightarrow {HNO}_3 + {HNO}_2$
ⓑ. $2{NO}_2 + 2{H}_2{O} \rightarrow 2{HNO}_3 + {H}_2$
ⓒ. $4{NO}_2({g}) + 2{H}_2{O}({l}) + {O}_2({g}) \rightarrow 4{HNO}_3({aq})$
ⓓ. ${NO}_2 + {H}_2{O} \rightarrow {HNO}_3 + {O}$
Correct Answer: $4{NO}_2({g}) + 2{H}_2{O}({l}) + {O}_2({g}) \rightarrow 4{HNO}_3({aq})$
Explanation: This equation correctly represents the stoichiometry of the overall reaction where ${NO}_2$, water, and atmospheric oxygen (${O}_2$) combine to yield ${Nitric Acid}$. This reaction happens either in the gaseous phase or within water droplets. ${HNO}_3$ is a strong acid and is responsible for a significant portion of the total acidity in acid rain, especially in areas with high vehicular traffic.
66. What is the primary adverse effect of acid rain on forest soil, particularly concerning plant nutrition?
ⓐ. Leaching of essential nutrients like ${Ca}^{2+}$ and ${Mg}^{2+}$ and release of toxic ${Al}^{3+}$ ions.
ⓑ. Increase in the basicity (${pH}$) of the soil.
ⓒ. Stimulation of nitrogen-fixing bacteria activity.
ⓓ. Rapid decomposition of organic matter, leading to increased fertility.
Correct Answer: Leaching of essential nutrients like ${Ca}^{2+}$ and ${Mg}^{2+}$ and release of toxic ${Al}^{3+}$ ions.
Explanation: The ${H}^{+}$ ions in acid rain replace essential nutrients like ${Ca}^{2+}$, ${Mg}^{2+}$, and ${K}^{+}$ on the soil particles, causing them to be washed away (leaching), which depletes soil fertility. The low ${pH}$ also mobilizes aluminum ions (${Al}^{3+}$) from soil minerals. These aluminum ions are highly toxic to plant roots and aquatic organisms.
67. Acid rain pollutants can travel hundreds of kilometres from their source before deposition occurs. This is an example of a characteristic environmental issue classified as:
ⓐ. Localized pollution.
ⓑ. Transboundary air pollution.
ⓒ. Point-source pollution.
ⓓ. Stratospheric transport.
Correct Answer: Transboundary air pollution.
Explanation: The precursor gases (${SO}_2$ and ${NO}_{{x}}$) are often emitted in one region (e.g., industrial area) but are carried by prevailing winds across great distances or national borders before they are chemically converted into acids and fall as rain in a different region. This widespread impact that crosses geopolitical boundaries defines it as transboundary air pollution, requiring international cooperation to control.
68. A scientist measures the ${pH}$ of two rain samples: Sample X has ${pH}=5.0$ and Sample Y has ${pH}=3.0$. By what factor is the hydrogen ion concentration ($[{H}^+]$) higher in Sample Y compared to Sample X?
ⓐ. $2$ times
ⓑ. $10$ times
ⓒ. $1000$ times
ⓓ. $100$ times
Correct Answer: $100$ times
Explanation: The ${pH}$ scale is logarithmic, where ${pH} = -\log[{H}^+]$. The difference between the ${pH}$ values is $\Delta{pH} = 5.0 – 3.0 = 2$. Therefore, the concentration difference in hydrogen ions ($[{H}^+]$) is calculated as $10^{\Delta{pH}}$.
$${Factor} = 10^{(5.0 – 3.0)} = 10^2 = 100$$
Sample Y (lower ${pH}$) is $\mathbf{100}$ times more acidic than Sample X.
69. The sudden and massive death of fish and other aquatic life in lakes during early spring is often linked to acid rain. This specific phenomenon is technically known as:
ⓐ. Eutrophication
ⓑ. Thermal shock
ⓒ. Acid shock
ⓓ. ${BOD}$ depletion
Correct Answer: Acid shock
Explanation: During winter, acidic pollutants are often trapped and concentrated in snow and ice. When temperatures rise rapidly in early spring, this accumulated acidic snow melts quickly and flows into the lake or stream. This rapid influx of concentrated acid causes a sudden and dramatic drop in the water’s ${pH}$, a phenomenon known as acid shock, which is lethal to the fish and other aquatic organisms, particularly those in the spawning stage.
70. Beyond direct toxicity, acid rain indirectly promotes a dangerous form of water pollution by:
ⓐ. Leaching toxic heavy metals (like ${Al}$, ${Hg}$, ${Pb}$) from the soil and sediment into water bodies.
ⓑ. Increasing the overall ${BOD}$ of the water body.
ⓒ. Precipitating heavy metal ions, making them harmless.
ⓓ. Stimulating algal growth, leading to eutrophication.
Correct Answer: Leaching toxic heavy metals (like ${Al}$, ${Hg}$, ${Pb}$) from the soil and sediment into water bodies.
Explanation: The high concentration of ${H}^{+}$ ions (low ${pH}$) in acid rain and subsequent surface runoff mobilizes metal ions that are usually insoluble and inert in soil and sediment. The acidity causes these highly toxic metals (especially Aluminum, Mercury, and Lead) to dissolve and leach into the aquatic environment. This secondary pollution process results in the poisoning of fish and can pose a severe health risk if the water is consumed.
71. In which layer of the atmosphere is the protective Ozone Layer, which shields the Earth from harmful UV radiation, primarily located?
ⓐ. Troposphere
ⓑ. Stratosphere
ⓒ. Mesosphere
ⓓ. Thermosphere
Correct Answer: Stratosphere
Explanation: The Ozone Layer (${O}_3$) is a region of high ozone concentration found primarily in the Stratosphere, extending roughly from $10{ km}$ to $50{ km}$ above the Earth’s surface, with the highest concentration usually between $15{ km}$ and $30{ km}$. This region’s existence is crucial for regulating the Earth’s temperature and protecting surface life.
72. The ozone layer acts as a natural shield by absorbing which specific part of the electromagnetic spectrum, thereby protecting living organisms from severe biological damage?
ⓐ. Infrared radiation
ⓑ. Visible light
ⓒ. Ultraviolet-B (UV-B) radiation
ⓓ. Microwaves
Correct Answer: Ultraviolet-B (UV-B) radiation
Explanation: Ozone molecules (${O}_3$) are highly efficient absorbers of high-energy Ultraviolet-B (${UV-B}$) radiation ($\sim 280{ to } 315{ nm}$). This absorption process protects the ${DNA}$ and proteins of living organisms, preventing a catastrophic increase in diseases like skin cancer and cataracts. Infrared radiation is absorbed primarily by greenhouse gases, contributing to global warming.
73. What is the main chemical species released from Chlorofluorocarbons (${CFCs}$) in the stratosphere that acts as a catalyst for ozone depletion?
ⓐ. Chlorine free radical (${Cl}^{\bullet}$)
ⓑ. Sulphur dioxide (${SO}_2$)
ⓒ. Carbon Dioxide (${CO}_2$)
ⓓ. Nitrous oxide (${N}_2{O}$)
Correct Answer: Chlorine free radical (${Cl}^{\bullet}$)
Explanation: Once ${CFCs}$ reach the stratosphere, high-energy UV radiation causes them to undergo photolysis, cleaving the Carbon-Chlorine (${C}-{Cl}$) bond and releasing a highly reactive Chlorine free radical (${Cl}^{\bullet}$). This radical is the species that initiates and sustains the catalytic cycle of ozone destruction.
74. What physical change must occur to a Chlorofluorocarbon (${CFC}$) molecule in the stratosphere before it can begin the catalytic destruction of ozone?
ⓐ. It must freeze inside polar stratospheric clouds (${PSCs}$).
ⓑ. It must react with ${H}_2{O}$ to form ${HCl}$.
ⓒ. It must be oxidized by atmospheric oxygen.
ⓓ. It must absorb high-energy ${UV}$ radiation, causing homolytic cleavage of the ${C}-{Cl}$ bond.
Correct Answer: It must absorb high-energy ${UV}$ radiation, causing homolytic cleavage of the ${C}-{Cl}$ bond.
Explanation: ${CFCs}$ are extremely stable in the troposphere. In the stratosphere, the high-energy ${UV}$ radiation provides the necessary energy ($h\nu$) to break the strong ${C}-{Cl}$ bond through photolysis (${CF}_2{Cl}_2 \xrightarrow{h\nu} {CF}_2{Cl}^{\bullet} + {Cl}^{\bullet}$), releasing the free radical. This step is essential for the ozone depletion mechanism to be activated.
75. The first step in the ozone destruction cycle catalyzed by a chlorine radical (${Cl}^{\bullet}$) is represented by the equation:
ⓐ. ${Cl}^{\bullet} + {O}_3 \rightarrow {ClO}^{\bullet} + {O}_2$
ⓑ. ${Cl}^{\bullet} + {O}_2 \rightarrow {ClO}_2^{\bullet}$
ⓒ. ${ClO}^{\bullet} + {O} \rightarrow {Cl}^{\bullet} + {O}_2$
ⓓ. ${O}_3 + {O} \rightarrow 2{O}_2$
Correct Answer: ${Cl}^{\bullet} + {O}_3 \rightarrow {ClO}^{\bullet} + {O}_2$
Explanation: The highly reactive chlorine radical (${Cl}^{\bullet}$) attacks the ozone molecule (${O}_3$), pulling off an oxygen atom. This forms a chlorine monoxide radical (${ClO}^{\bullet}$) and a molecule of molecular oxygen (${O}_2$). The subsequent step (Option C) regenerates the ${Cl}^{\bullet}$, allowing a single chlorine atom to destroy thousands of ozone molecules catalytically.
76. What property of ${CFCs}$ allows them to survive the troposphere without being broken down by rain or chemical reactions, enabling them to eventually reach the stratosphere?
ⓐ. High solubility in water (Hydrophilic nature)
ⓑ. High reactivity with common atmospheric oxidants (${OH}^{\bullet}$)
ⓒ. Low molecular weight and high volatility
ⓓ. Extreme chemical inertness and stability
Correct Answer: Extreme chemical inertness and stability
Explanation: ${CFCs}$ are chemically inert, meaning they are non-reactive with most common tropospheric species, including water and free radicals. This inertness gives them a long atmospheric lifetime (up to $100$ years), allowing them sufficient time to diffuse slowly up into the stratosphere where they are finally broken down by high-energy ${UV}$ radiation.
77. The term “Ozone Hole,” often used to describe severe depletion, is defined scientifically as:
ⓐ. The complete, permanent absence of ozone gas over the South Pole.
ⓑ. A region in the stratosphere where the ozone concentration falls below $220{ Dobson Units (DU)}$.
ⓒ. A naturally occurring, temporary thinning of ozone due to solar activity.
ⓓ. A tear in the ozone layer caused by supersonic aircraft.
Correct Answer: A region in the stratosphere where the ozone concentration falls below $220{ Dobson Units (DU)}$.
Explanation: The “Ozone Hole” is a dramatic thinning, not a void. Scientists define the boundary of the ozone hole as the geographical area where the total column ozone measurement drops below the critical threshold of $220{ Dobson Units (DU)}$, which historically occurs most severely over Antarctica during the Southern Hemisphere spring.
78. Increased ${UV-B}$ radiation reaching the Earth’s surface due to ozone depletion poses the most significant health risk in the form of:
ⓐ. Respiratory diseases like ${COPD}$.
ⓑ. Neurological disorders and loss of memory.
ⓒ. Skin cancer (melanoma and non-melanoma) and cataracts.
ⓓ. Chronic liver and kidney damage.
Correct Answer: Skin cancer (melanoma and non-melanoma) and cataracts.
Explanation: ${UV-B}$ radiation is highly energetic and can penetrate skin and eyes, damaging ${DNA}$. Increased exposure is directly correlated with a higher incidence of skin cancer (the most serious being melanoma) and the clouding of the eye lens, known as cataracts, making these the primary human health concerns related to ozone depletion.
79. The natural process of ozone (${O}_3$) formation in the stratosphere is represented by the overall equation:
ⓐ. ${O}_2 + {UV} \rightarrow 2{O}^{\bullet}$
ⓑ. ${O}^{\bullet} + {O}_2 + {M} \rightarrow {O}_3 + {M}^{*}$
ⓒ. ${O}_3 + {O}^{\bullet} \rightarrow 2{O}_2$
ⓓ. ${O}_3 + {UV} \rightarrow {O}_2 + {O}^{\bullet}$
Correct Answer: ${O}^{\bullet} + {O}_2 + {M} \rightarrow {O}_3 + {M}^{*}$
Explanation: The formation of ozone involves an oxygen atom (${O}^{\bullet}$), produced by the photolysis of ${O}_2$ (Option A), reacting with an oxygen molecule (${O}_2$). The third body (${M}$, typically ${N}_2$ or ${O}_2$) is necessary to absorb the excess energy of the reaction (${M}^{*}$ represents the energized third body), thus stabilizing the newly formed ${O}_3$ molecule and completing the formation process in the stratosphere.
80. The most significant and successful international agreement designed to phase out the production of ozone-depleting substances (${ODS}$) like ${CFCs}$ is the:
ⓐ. Montreal Protocol
ⓑ. Kyoto Protocol
ⓒ. Paris Agreement
ⓓ. Vienna Convention
Correct Answer: Montreal Protocol
Explanation: The Montreal Protocol on Substances that Deplete the Ozone Layer is a landmark international treaty established in $1987$. It set mandatory schedules for countries to reduce and eventually eliminate the production and consumption of ${ODS}$ (${CFCs}$, ${Halons}$, etc.). The success of this protocol is evidenced by the slowing of the ozone depletion trend and the gradual recovery of the ozone layer.
81. Besides ${CFCs}$, which other class of compounds primarily found in agricultural emissions and high-altitude aircraft exhaust acts as a precursor for ozone-depleting ${NO}_{{x}}$ radicals in the stratosphere?
ⓐ. Carbon Monoxide (${CO}$)
ⓑ. Methane (${CH}_4$)
ⓒ. Nitrous Oxide (${N}_2{O}$)
ⓓ. Sulphur Dioxide (${SO}_2$)
Correct Answer: Nitrous Oxide (${N}_2{O}$)
Explanation: Nitrous Oxide (${N}_2{O}$), a potent greenhouse gas primarily released from nitrogen fertilizers and industrial processes, is highly stable. It diffuses into the stratosphere, where it reacts with oxygen atoms to produce ${NO}$ (Nitric Oxide) radicals (${N}_2{O} + {O}^{\bullet} \rightarrow 2{NO}^{\bullet}$). The ${NO}$ radical then participates in the catalytic destruction of ozone, similar to the chlorine radical.
82. The ozone destruction cycle catalyzed by a chlorine monoxide radical (${ClO}^{\bullet}$) involves a second step where the chlorine radical (${Cl}^{\bullet}$) is regenerated. This regeneration step is:
ⓐ. ${Cl}^{\bullet} + {O}_3 \rightarrow {ClO}^{\bullet} + {O}_2$
ⓑ. ${ClO}^{\bullet} + {O}^{\bullet} \rightarrow {Cl}^{\bullet} + {O}_2$
ⓒ. $2{O}_3 \rightarrow 3{O}_2$
ⓓ. ${CF}_2{Cl}_2 \xrightarrow{h\nu} {CF}_2{Cl}^{\bullet} + {Cl}^{\bullet}$
Correct Answer: ${ClO}^{\bullet} + {O}^{\bullet} \rightarrow {Cl}^{\bullet} + {O}_2$
Explanation: The catalytic cycle involves two main steps. Step 1: ${Cl}^{\bullet}$ destroys ${O}_3$, forming ${ClO}^{\bullet}$ and ${O}_2$. Step 2 (the regeneration step): The ${ClO}^{\bullet}$ radical reacts with an atomic oxygen (${O}^{\bullet}$), regenerating the highly destructive ${Cl}^{\bullet}$ radical and forming another ${O}_2$ molecule. This regeneration ensures that the chlorine atom can destroy thousands of ${O}_3$ molecules before being sequestered.
83. Which of the following conditions, unique to the Antarctic stratosphere during winter, is essential for accelerating the massive, seasonal destruction of the ozone layer?
ⓐ. High temperatures and lack of sunlight.
ⓑ. The formation of Polar Stratospheric Clouds (${PSCs}$).
ⓒ. High concentration of volcanic ash.
ⓓ. High humidity and fog formation.
Correct Answer: The formation of Polar Stratospheric Clouds (${PSCs}$).
Explanation: During the extremely cold Antarctic winter, stable air currents create a polar vortex, allowing temperatures to drop low enough ($\sim -78^{\circ}{C}$). This enables the formation of Polar Stratospheric Clouds (${PSCs}$). These ice-crystal surfaces act as heterogeneous reaction sites where relatively inert chlorine reservoirs (like ${HCl}$ and ${ClONO}_2$) are converted into highly reactive, ozone-depleting molecules (like ${Cl}_2$), which are then released when sunlight returns in spring.
84. The overall net reaction for the catalytic destruction of ozone by chlorine is:
ⓐ. ${Cl}^{\bullet} + {O}_3 + {O}^{\bullet} \rightarrow {Cl}^{\bullet} + 2{O}_2$
ⓑ. ${Cl}^{\bullet} + {O}_3 \rightarrow {ClO}^{\bullet} + {O}_2$
ⓒ. $2{O}_3 \rightarrow 3{O}_2$
ⓓ. ${O}_3 + {O}^{\bullet} \rightarrow 2{O}_2$
Correct Answer: ${O}_3 + {O}^{\bullet} \rightarrow 2{O}_2$
Explanation: The overall net reaction of the catalytic cycle is obtained by summing the two main steps and cancelling out the intermediate species (${Cl}^{\bullet}$ and ${ClO}^{\bullet}$).
$${Cl}^{\bullet} + {O}_3 \rightarrow {ClO}^{\bullet} + {O}_2$$
$${ClO}^{\bullet} + {O}^{\bullet} \rightarrow {Cl}^{\bullet} + {O}_2$$
$${Net: }{O}_3 + {O}^{\bullet} \rightarrow 2{O}_2$$
The net effect is the conversion of an ozone molecule and an oxygen atom (which would normally react to form ozone) into two molecules of molecular oxygen.
85. ${Halons}$ are effective fire extinguishing agents but pose a severe risk to the ozone layer. This class of compounds contains which highly efficient ozone-depleting element in addition to chlorine?
ⓐ. Fluorine
ⓑ. Sulphur
ⓒ. Bromine
ⓓ. Iodine
Correct Answer: Bromine
Explanation: Halons are Haloalkanes that contain Bromine (bromofluorocarbons or bromochlorofluorocarbons). Bromine radicals (${Br}^{\bullet}$) are released in the stratosphere through photolysis, and they are estimated to be 40 to 100 times more effective at destroying ozone than chlorine radicals on a per-atom basis. Halons were included in the phase-out schedule of the Montreal Protocol due to this extreme potency.
86. The natural process that temporarily removes or sequesters ozone-depleting chlorine radicals (${Cl}^{\bullet}$) from the stratosphere, converting them into relatively harmless reservoir species, is the reaction between ${Cl}^{\bullet}$ and:
ⓐ. Oxygen gas (${O}_2$)
ⓑ. Nitric Oxide (${NO}$)
ⓒ. Methane (${CH}_4$) or ${Nitrogen Dioxide}$ (${NO}_2$)
ⓓ. Carbon Dioxide (${CO}_2$)
Correct Answer: Methane (${CH}_4$) or ${Nitrogen Dioxide}$ (${NO}_2$)
Explanation: Chlorine radicals are removed when they react with other trace gases to form stable molecules known as reservoir species. For instance, ${Cl}^{\bullet}$ reacts with Methane (${CH}_4$) to form ${HCl}$ (${Cl}^{\bullet} + {CH}_4 \rightarrow {HCl} + {CH}_3^{\bullet}$). ${ClO}^{\bullet}$ reacts with ${NO}_2$ to form chlorine nitrate (${ClONO}_2$). These reservoir species are temporarily inactive but can be reactivated on the surface of ${PSCs}$.
87. Which of the following wavelength ranges of ${UV}$ radiation is known to have the highest energy and is almost entirely absorbed by the stratosphere’s oxygen (${O}_2$) and ozone (${O}_3$)?
ⓐ. ${UV-B}$ ($280{-}315{ nm}$)
ⓑ. ${UV-C}$ ($100{-}280{ nm}$)
ⓒ. ${UV-A}$ ($315{-}400{ nm}$)
ⓓ. Visible Light ($400{-}700{ nm}$)
Correct Answer: ${UV-C}$ ($100{-}280{ nm}$)
Explanation: ${UV-C}$ radiation is the most energetic part of the UV spectrum. It is completely absorbed by molecular oxygen (${O}_2$) and ozone (${O}_3$) high in the stratosphere. ${UV-B}$ is partially absorbed by ${O}_3$ (the one causing ozone depletion damage). ${UV-A}$ is mostly transmitted to the Earth’s surface.
88. The most efficient way to reduce the impact of stratospheric pollution by ${CFCs}$ and ${Halons}$ is:
ⓐ. Strict global controls and phase-out of their production and use.
ⓑ. Designing new filters for industrial smokestacks.
ⓒ. Injecting chemical neutralizers directly into the stratosphere.
ⓓ. Increasing the altitude of commercial aircraft.
Correct Answer: Strict global controls and phase-out of their production and use.
Explanation: Since ${CFCs}$ and ${Halons}$ have atmospheric lifetimes measured in decades to centuries and are chemically inert in the troposphere, the only effective long-term solution is to stop emitting them at the source. The Montreal Protocol successfully implemented this global phase-out, proving that source control is the most effective environmental strategy for stratospheric pollutants.
89. ${Halogen}$ atoms like chlorine and bromine are extremely damaging to ozone because they are:
ⓐ. Used up permanently after one ozone destruction reaction.
ⓑ. Primary pollutants that form quickly from ${CO}_2$ and ${H}_2{O}$.
ⓒ. Heavier than ozone, causing them to sink and collect in the lower stratosphere.
ⓓ. Catalytic, meaning they are regenerated and can destroy thousands of ozone molecules.
Correct Answer: Catalytic, meaning they are regenerated and can destroy thousands of ozone molecules.
Explanation: The key feature of ${Cl}^{\bullet}$ and ${Br}^{\bullet}$ is their catalytic nature. They are reactants in the ozone destruction process but are reformed in the second step of the cycle (${ClO}^{\bullet} + {O}^{\bullet} \rightarrow {Cl}^{\bullet} + {O}_2$). Because they are not consumed in the overall reaction, a single radical can continue to destroy ozone molecules for many years, leading to exponential depletion.
90. In the Antarctic stratosphere, the presence of Polar Stratospheric Clouds (${PSCs}$) catalyzes which crucial conversion that sets the stage for the ozone hole formation in spring?
ⓐ. Inactive chlorine reservoirs (${HCl}, {ClONO}_2$) into highly reactive free chlorine (${Cl}_2$).
ⓑ. ${CFCs}$ into ${O}_3$.
ⓒ. ${O}_3$ into harmless ${N}_2$.
ⓓ. ${SO}_2$ into ${H}_2{SO}_4$.
Correct Answer: Inactive chlorine reservoirs (${HCl}, {ClONO}_2$) into highly reactive free chlorine (${Cl}_2$).
Explanation: During the dark, cold winter inside the polar vortex, ${HCl}$ and ${ClONO}_2$ condense onto the frozen surfaces of ${PSCs}$. Heterogeneous reactions on these surfaces convert these inactive reservoir compounds into photolytically unstable species like molecular chlorine (${Cl}_2$). When sunlight returns in spring, ${Cl}_2$ is rapidly photolyzed into ${Cl}^{\bullet}$ radicals, causing rapid, massive ozone depletion.
91. The natural process of ozone formation in the stratosphere is an equilibrium process known as the Chapman Cycle. The overall effect of this cycle is to convert which form of energy into heat, regulating stratospheric temperature?
ⓐ. Chemical potential energy
ⓑ. Infrared (heat) radiation
ⓒ. Kinetic energy of gas molecules
ⓓ. High-energy ${UV-C}$ radiation
Correct Answer: High-energy ${UV-C}$ radiation
Explanation: The Chapman Cycle begins with the photolysis of oxygen molecules (${O}_2$) by ${UV-C}$ radiation to form two oxygen atoms (${O}^{\bullet}$). These atoms then combine with ${O}_2$ to form ${O}_3$. The energy of the absorbed ${UV-C}$ radiation is effectively converted into heat during the bond-forming step (${O}^{\bullet} + {O}_2 \rightarrow {O}_3$). This conversion is why the temperature of the stratosphere increases with altitude, making the ozone layer vital for atmospheric stability and temperature regulation.
92. The formation of ozone (${O}_3$) from molecular oxygen (${O}_2$) is an exothermic process. Which chemical equation represents the first step of ozone formation in the Chapman Cycle?
ⓐ. ${O}_3 + {O} \rightarrow 2{O}_2$
ⓑ. ${O}_2({g}) + h\nu ({UV-C}) \rightarrow 2{O}^{\bullet}({g})$
ⓒ. ${O}^{\bullet} + {O}_2 + {M} \rightarrow {O}_3 + {M}^{*}$
ⓓ. ${O}_3 + h\nu ({UV-B}) \rightarrow {O}_2 + {O}^{\bullet}$
Correct Answer: ${O}_2({g}) + h\nu ({UV-C}) \rightarrow 2{O}^{\bullet}({g})$
Explanation: The first step in the natural cycle is the photolysis of molecular oxygen (${O}_2$). Highly energetic ${UV-C}$ radiation ($h\nu$) provides the energy to break the double bond in ${O}_2$, yielding two highly reactive atomic oxygen free radicals (${O}^{\bullet}$). These radicals are essential for the subsequent formation of ${O}_3$.
93. A major consequence of increased ${UV-B}$ radiation reaching the Earth’s surface due to ozone depletion is its effect on marine life. This effect primarily involves damage to:
ⓐ. Large marine mammals like whales and seals.
ⓑ. Deep-sea benthic organisms.
ⓒ. Phytoplankton, the base of the marine food chain.
ⓓ. Coral reefs through bleaching.
Correct Answer: Phytoplankton, the base of the marine food chain.
Explanation: Phytoplankton are microscopic, single-celled organisms that perform photosynthesis and form the base of the entire marine food web. They are extremely sensitive to ${UV-B}$ radiation. Increased ${UV-B}$ exposure can inhibit their growth, damage their ${DNA}$, and reduce their photosynthetic efficiency, leading to a collapse in the marine food chain and a decrease in the ocean’s ability to absorb ${CO}_2$.
94. Which of the following is an effect of ozone layer depletion on terrestrial plants and agriculture?
ⓐ. Reduced water requirement of plants.
ⓑ. Increased rate of photolysis in leaves.
ⓒ. Stimulation of photosynthesis leading to higher crop yields.
ⓓ. Inhibition of plant growth and damage to ${DNA}$ and proteins.
Correct Answer: Inhibition of plant growth and damage to ${DNA}$ and proteins.
Explanation: Excessive ${UV-B}$ radiation negatively impacts plant physiology. It can damage the nucleic acids (${DNA}$), proteins, and cell membranes within the plant, leading to stunted growth, reduced leaf size, and lower photosynthetic rates, which ultimately results in a decrease in agricultural yield.
95. When scientists measure the concentration of ozone in the total atmospheric column above a point on Earth, the standard unit used is the:
ⓐ. Pascal (${Pa}$)
ⓑ. Parts per million (${ppm}$)
ⓒ. Dobson Unit (${DU}$)
ⓓ. Mole per litre (${mol}{ L}^{-1}$)
Correct Answer: Dobson Unit (${DU}$)
Explanation: The Dobson Unit (${DU}$) is the primary unit for measuring the total column ozone concentration. One ${DU}$ corresponds to the thickness of a layer of pure ozone that would be formed if all the ozone over a given point were brought down to standard temperature and pressure ($0^{\circ}{C}$ and $1{ atm}$); $1{ DU}$ is defined as $0.01{ mm}$ thickness.
96. The increase in ${UV-B}$ radiation due to ozone depletion can weaken the immune system in humans, leading to:
ⓐ. Increased blood pressure.
ⓑ. Increased susceptibility to infectious diseases.
ⓒ. Decrease in the body’s natural antioxidant levels.
ⓓ. Permanent loss of body heat regulation.
Correct Answer: Increased susceptibility to infectious diseases.
Explanation: ${UV-B}$ exposure can suppress the human body’s immune response, particularly the defense mechanisms in the skin. This immunosuppression makes individuals more vulnerable to infectious diseases, including those transmitted through the skin, and can reduce the effectiveness of vaccinations.
97. What is the fundamental role of the stratosphere’s ozone layer (${O}_3$) concerning the planet’s energy budget?
ⓐ. It absorbs ${UV-C}$ and ${UV-B}$ radiation, preventing it from reaching the surface.
ⓑ. It reflects all incoming visible light back into space.
ⓒ. It acts as a blanket, trapping outgoing infrared radiation (${IR}$).
ⓓ. It chemically converts ${CO}_2$ into ${O}_2$ through photolysis.
Correct Answer: It absorbs ${UV-C}$ and ${UV-B}$ radiation, preventing it from reaching the surface.
Explanation: The most critical function of the ozone layer is its ability to absorb most of the Sun’s harmful ${UV-C}$ (all of it) and most of the ${UV-B}$ radiation. This absorption protects life and is also responsible for the temperature inversion (heating) observed in the stratosphere. Option C is the role of tropospheric greenhouse gases.
98. Which ozone-depleting substance has a high Ozone Depletion Potential (${ODP}$) because it contains three chlorine atoms and was historically used in solvents and fire extinguishers?
ⓐ. ${CFC-12}$ (${CF}_2{Cl}_2$)
ⓑ. ${HFC-134a}$ (${CH}_2{FCF}_3$)
ⓒ. Carbon Tetrachloride (${CCl}_4$)
ⓓ. Methane (${CH}_4$)
Correct Answer: Carbon Tetrachloride (${CCl}_4$)
Explanation: Carbon Tetrachloride (${CCl}_4$) is a potent ${ODS}$ because it contains four chlorine atoms, three of which are easily released as radicals upon photolysis in the stratosphere. While not a ${CFC}$, it is a major man-made source of stratospheric chlorine and was widely used as a cleaning solvent and fire retardant before being phased out under the Montreal Protocol.
99. The ozone destruction process is a chain reaction where a single chlorine radical can destroy many ${O}_3$ molecules before it is finally removed from the cycle. This makes the reaction:
ⓐ. Catalytic with a high turnover rate. S
ⓑ. pontaneous and reversible.
ⓒ. Highly dependent on low ${NO}_{{x}}$ concentrations.
ⓓ. Endothermic, requiring constant energy input.
Correct Answer: Catalytic with a high turnover rate.
Explanation: The process is catalytic because the chlorine radical (${Cl}^{\bullet}$) that starts the reaction is regenerated in the second step (${ClO}^{\bullet} + {O}^{\bullet} \rightarrow {Cl}^{\bullet} + {O}_2$). Since the catalyst is not consumed, a single ${Cl}$ atom can rapidly destroy ${O}_3$ molecules, leading to a high turnover rate (efficiency) and massive depletion.
100. In addition to skin cancer and cataracts, increased ${UV-B}$ radiation is harmful to polymer materials and paints used in construction and vehicles, causing them to:
ⓐ. Become highly flammable.
ⓑ. Absorb water and swell rapidly.
ⓒ. Degrade, embrittle, and lose their strength and color.
ⓓ. Increase their ${CO}_2$ absorption capacity.
Correct Answer: Degrade, embrittle, and lose their strength and color.
Explanation: ${UV-B}$ radiation is very energetic and can break the chemical bonds in many synthetic and natural polymers (plastics, rubber, nylon) and surface coatings (paints). This damage manifests as embrittlement, cracking, loss of mechanical strength, and fading of color, leading to a shortening of the useful lifespan of materials exposed to sunlight.
Welcome to Class 11 Chemistry MCQs – Chapter 14: Environmental Chemistry (Part of 3). This chapter is crucial for understanding the impact of chemistry on the environment and covers various concepts related to pollution, green chemistry, and sustainable practices. Whether you are preparing for your Board exams, JEE, NEET, or state-level tests, this chapter is essential for scoring well in both theory and practical-based questions.
Navigation & parts: This chapter contains a total of 267 MCQs in 3 parts (100 + 100 + 67), with this page dedicated to the first set of 100 MCQs covering a wide range of environmental chemistry topics, including air and water pollution, green chemistry principles, and environmental protection. Keep navigating through the other parts for complete practice.
What you will learn & practice (Chapter 14: Environmental Chemistry)
- Air pollution and its effects on human health, ecosystems, and the atmosphere
- Water pollution—sources, effects, and treatment methods like sewage treatment and eutrophication
- Greenhouse gases and their role in climate change, including CO2, methane, and nitrous oxide
- Ozone layer depletion and the environmental impacts of CFCs
- Solid waste management, recycling, and disposal techniques
- Biodegradable vs non-biodegradable waste and their impact on the environment
- Environmental sustainability and the role of green chemistry in minimizing pollution
- Water treatment methods: desalination, filtration, and chemical treatments
- Pollution control methods: electrostatic precipitators, scrubbers, and catalytic converters
- Environmental impact assessment and its importance in industrial practices
How to use this site to master Environmental Chemistry MCQs
- Warm-up (10 mins): Review the key topics above and prepare your formula sheet for common pollutants and their effects.
- Active attempt: Solve 10–20 MCQs at a time. After each question, read the feedback thoroughly to understand why your answer was right or wrong.
- Build your personal deck: Use the ❤️ Heart button on any MCQ to mark it as a Favourite for later review. Use the Favourite Toggle to quickly view your marked questions.
- Write it your way: Use the Workspace button to jot down quick notes or formulas for any difficult question. Your notes will auto-save for future reference.
- Shuffle & strengthen: Use the Random button to shuffle questions and practice recalling information in a variety of formats.
- Smart revision plan: Revisit your Favourite list at spaced intervals (Day 2, Day 4, and Day 7) to ensure long-term retention. Use the Workspace notes for quick revision before exams.
Why this helps for Boards, JEE Main & NEET
- Boards: Many environmental chemistry questions are based on case studies and real-life applications—master these concepts for scoring in theory exams.
- JEE Main/Advanced: Numerical problems related to pollution, chemical reactions in environmental processes, and treatment methods are common.
- NEET: Understanding environmental chemistry topics is crucial for concept-based MCQs, especially questions related to air/water pollution and sustainability.
- Your edge: The Favourite and Workspace features help you organize, mark important questions, and build a personal revision set for last-minute prep.
Common mistakes to avoid
- Mixing up types of pollutants (primary vs secondary, organic vs inorganic) and their impact on human health
- Not understanding green chemistry principles and how they apply to sustainable industrial practices
- Forgetting the steps in water treatment—ensure you know the full process of filtration and chemical treatment
- Overlooking solid waste management methods and recycling processes
- Not being clear on ozone depletion—understand the role of CFCs and the consequences for the environment
You’re on the right track! Use this page as your study hub, marking important questions with ❤️, jotting notes in Workspace, and revisiting them for focused revision. Environmental chemistry can seem overwhelming, but with the right approach, you’ll master it in no time.
Explore more: Class 11 Chemistry – Chapter Index, Class 11 – Subject Index, All Classes – MCQ Library.
Quick FAQ
What is environmental chemistry?
Environmental chemistry focuses on studying the chemical processes in the environment, including the pollution caused by chemicals, their effects, and methods of mitigation.
How many MCQs should I practice per day?
It’s recommended to start with 20–30 MCQs daily, focusing on understanding the concepts behind each question. Increase the number if you have more time.
How can I use this site for last-minute revision?
Use the Favourite Toggle to quickly review all marked questions. Revisit your Workspace notes to ensure you don’t miss important concepts.
- 👉 Total MCQs in this chapter: 267 (100 + 100 + 67)
- 👉 This page: First 100 MCQs with answers & explanations
- 👉 Best for: Boards • JEE/NEET • Environmental Chemistry practice • concept revision • quick quizzes
- 👉 Next: Continue with Part 2 for more practice
FAQs on Environmental Chemistry ▼
▸ What are Environmental Chemistry MCQs in Class 11 Chemistry?
These are multiple-choice questions from Chapter 14 of NCERT Class 11 Chemistry – Environmental Chemistry. They focus on environmental issues like pollution, green chemistry, environmental impact, and sustainable development.
▸ How many MCQs are available in this chapter?
There are a total of 267 Environmental Chemistry MCQs. They are divided into 3 structured parts – two sets of 100 questions each and one set of 67 questions.
▸ Are Environmental Chemistry MCQs important for JEE and NEET?
Yes, this chapter is significant for JEE and NEET. Key topics include air and water pollution, ozone depletion, green chemistry, and the role of chemistry in environmental protection, which are frequently covered in entrance exams.
▸ Do these MCQs include correct answers and explanations?
Yes, each MCQ is provided with the correct answer along with detailed explanations, ensuring that students understand the concepts thoroughly.
▸ Which subtopics are covered in these Environmental Chemistry MCQs?
These MCQs cover essential subtopics like air pollution, water pollution, green chemistry, the role of chemistry in reducing environmental impact, the depletion of ozone layer, and waste management practices.