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1. Hydrogen is placed separately in the periodic table because:
ⓐ. It resembles alkali metals only.
ⓑ. It resembles halogens only.
ⓒ. It shows no similarity with any group.
ⓓ. It shows similarities with both alkali metals and halogens.
Correct Answer: It shows similarities with both alkali metals and halogens.
Explanation: Hydrogen has one electron like alkali metals (Group 1) and forms $H^+$ ion. However, like halogens (Group 17), it is diatomic and can gain an electron to form $H^-$. Thus, its dual character makes it unique and difficult to place in a single group of the periodic table.
2. Which of the following statements about hydrogen is correct?
ⓐ. Hydrogen is a metal.
ⓑ. Hydrogen always acts as a reducing agent.
ⓒ. Hydrogen can act both as an oxidising and a reducing agent.
ⓓ. Hydrogen never reacts with metals.
Correct Answer: Hydrogen can act both as an oxidising and a reducing agent.
Explanation: In reactions with metals such as $Na + H_2 \rightarrow NaH$, hydrogen acts as an oxidising agent. With non-metals like $H_2 + Cl_2 \rightarrow 2HCl$, it acts as a reducing agent. Hence, hydrogen exhibits dual chemical behavior.
3. What is the most abundant element in the universe?
ⓐ. Oxygen
ⓑ. Nitrogen
ⓒ. Hydrogen
ⓓ. Carbon
Correct Answer: Hydrogen
Explanation: Hydrogen constitutes about 70–75% of the total mass of the universe. It is found in stars, planets, and interstellar gases. It is the primary element formed after the Big Bang, making it the most abundant element known.
4. Which of the following is a common industrial method for producing hydrogen?
ⓐ. Electrolysis of water
ⓑ. Photosynthesis
ⓒ. Haber’s process
ⓓ. Solvay process
Correct Answer: Electrolysis of water
Explanation: Electrolysis of water is a clean method to produce hydrogen gas. Electric current decomposes water into hydrogen and oxygen gases:
$2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$.
This method produces pure hydrogen, though it is energy-intensive compared to industrial steam reforming.
5. Which form of hydrogen is most stable under normal conditions?
ⓐ. Atomic hydrogen
ⓑ. Dihydrogen ($H_2$)
ⓒ. Ionic hydrogen
ⓓ. Nascent hydrogen
Correct Answer: Dihydrogen ($H_2$)
Explanation: Molecular hydrogen ($H_2$) is stable because two hydrogen atoms share electrons to form a covalent bond, completing each atom’s 1s shell. Atomic or nascent hydrogen is highly reactive and exists only transiently.
6. The electronic configuration of hydrogen is:
ⓐ. $1s^2$
ⓑ. $1s^1$
ⓒ. $2s^1$
ⓓ. $1s^22s^1$
Correct Answer: $1s^1$
Explanation: Hydrogen has one proton and one electron. The single electron occupies the 1s orbital, so its configuration is $1s^1$. This configuration explains its resemblance to alkali metals, which also have one valence electron.
7. Hydrogen gas is collected by:
ⓐ. Upward displacement of water
ⓑ. Downward displacement of water
ⓒ. Downward displacement of air
ⓓ. Upward displacement of air
Correct Answer: Upward displacement of water
Explanation: Hydrogen is lighter than air and insoluble in water. Therefore, it is collected by the upward displacement of water. The other methods are used for gases heavier than air or soluble in water, like $CO_2$ or $HCl$.
8. Which of the following is NOT a property of hydrogen?
ⓐ. It is colourless and odourless.
ⓑ. It burns in air with a pale blue flame.
ⓒ. It supports combustion.
ⓓ. It is the lightest known gas.
Correct Answer: It supports combustion.
Explanation: Hydrogen is a combustible gas but does not support combustion. It burns in oxygen to form water: $2H_2 + O_2 \rightarrow 2H_2O$. Hence, it itself burns but cannot support burning of other substances.
9. In which form does hydrogen exist in the sun and stars?
ⓐ. Molecular hydrogen ($H_2$)
ⓑ. Atomic hydrogen
ⓒ. Hydride form
ⓓ. Ionized hydrogen ($H^+$)
Correct Answer: Ionized hydrogen ($H^+$)
Explanation: In the extremely high temperatures of the sun and stars, hydrogen atoms are ionized into protons ($H^+$) and electrons. The fusion of these protons leads to the production of helium and massive energy release through nuclear fusion.
10. What is the main industrial use of hydrogen?
ⓐ. In the manufacture of fertilizers
ⓑ. As a laboratory reagent
ⓒ. For cleaning metals
ⓓ. For lighting lamps
Correct Answer: In the manufacture of fertilizers
Explanation: Hydrogen is primarily used in the Haber process to synthesize ammonia:
$N_2 + 3H_2 \rightarrow 2NH_3$.
Ammonia is a key raw material for producing fertilizers like urea and ammonium nitrate. Hence, hydrogen plays a vital role in agriculture and industrial chemistry.
11. Which property of hydrogen is similar to that of alkali metals?
ⓐ. It has two electrons in its outermost shell.
ⓑ. It forms monovalent positive ions.
ⓒ. It readily forms covalent halides.
ⓓ. It shows variable oxidation states.
Correct Answer: It forms monovalent positive ions.
Explanation: Like alkali metals (e.g., Na → Na⁺), hydrogen also loses its single electron to form the monovalent ion $H^+$. This similarity is due to their common $ns^1$ electronic configuration, where $n=1$ for hydrogen and $n>1$ for alkali metals.
12. Hydrogen and alkali metals both:
ⓐ. Are solid under normal conditions.
ⓑ. Have high ionization enthalpy.
ⓒ. React with non-metals to form ionic compounds.
ⓓ. Are good conductors of electricity.
Correct Answer: React with non-metals to form ionic compounds.
Explanation: Alkali metals react with halogens to form ionic halides, e.g., $2Na + Cl_2 \rightarrow 2NaCl$. Similarly, hydrogen reacts with halogens to form hydrogen halides, e.g., $H_2 + Cl_2 \rightarrow 2HCl$. These reactions show the resemblance between hydrogen and Group 1 elements.
13. What is the main difference between hydrogen and alkali metals despite their similarities?
ⓐ. Hydrogen cannot lose its electron.
ⓑ. Hydrogen is non-metallic, while alkali metals are metallic.
ⓒ. Hydrogen has more electrons than alkali metals.
ⓓ. Hydrogen forms colored compounds like transition metals.
Correct Answer: Hydrogen is non-metallic, while alkali metals are metallic.
Explanation: Hydrogen behaves as a non-metal and exists as a gas at room temperature. In contrast, alkali metals are soft, metallic solids with high electrical conductivity. This fundamental difference distinguishes hydrogen from alkali metals.
14. Which of the following statements best describes the electronic configuration similarity between hydrogen and alkali metals?
ⓐ. Both have one electron in the $p$-orbital.
ⓑ. Both have one electron in the $d$-orbital.
ⓒ. Both have a completely filled shell.
ⓓ. Both have one electron in the outermost $s$-orbital.
Correct Answer: Both have one electron in the outermost $s$-orbital.
Explanation: Hydrogen has the configuration $1s^1$, while alkali metals have $ns^1$. This similar outer configuration accounts for many of their common properties, such as forming $+1$ ions and reacting with halogens.
15. Which compound of hydrogen is analogous to sodium chloride in terms of ionic nature?
ⓐ. $HCl$
ⓑ. $H_2O$
ⓒ. $NH_3$
ⓓ. $NaH$
Correct Answer: $NaH$
Explanation: Sodium hydride ($NaH$) is an ionic compound similar to sodium chloride ($NaCl$). In $NaH$, sodium donates an electron to hydrogen forming $Na^+$ and $H^-$. This behavior of forming an ionic bond shows hydrogen’s resemblance to halogens and alkali metals in bonding nature.
16. Both hydrogen and alkali metals:
ⓐ. Form strong basic oxides.
ⓑ. Form halides with similar stoichiometry.
ⓒ. Are non-reactive toward oxygen.
ⓓ. Form volatile molecular compounds.
Correct Answer: Form halides with similar stoichiometry.
Explanation: Hydrogen forms halides like $HCl$, and alkali metals form $NaCl$, both having the same 1:1 stoichiometric ratio. This similarity arises because both hydrogen and alkali metals exhibit a valency of +1 when combined with halogens.
17. Why does hydrogen resemble alkali metals in terms of oxidation number?
ⓐ. It can attain +1 oxidation state by losing one electron.
ⓑ. It can attain +2 oxidation state by losing two electrons.
ⓒ. It cannot lose electrons at all.
ⓓ. It always acts as a reducing agent.
Correct Answer: It can attain +1 oxidation state by losing one electron.
Explanation: Hydrogen ($1s^1$) can lose its only electron to form $H^+$, achieving the oxidation state of +1, the same as alkali metals such as sodium and potassium in their compounds like $NaCl$ and $KBr$.
18. Hydrogen shows similarity to alkali metals in which of the following reactions?
ⓐ. $H_2 + Cl_2 \rightarrow 2HCl$
ⓑ. $2H_2O \rightarrow 2H_2 + O_2$
ⓒ. $2Na + 2H_2O \rightarrow 2NaOH + H_2$
ⓓ. $H_2 + N_2 \rightarrow 2NH_3$
Correct Answer: $H_2 + Cl_2 \rightarrow 2HCl$
Explanation: Just like alkali metals react with halogens to form halides ($Na + Cl_2 \rightarrow 2NaCl$), hydrogen reacts with chlorine to form hydrogen chloride gas ($H_2 + Cl_2 \rightarrow 2HCl$). This demonstrates their analogous reactivity pattern.
19. Which of the following properties does hydrogen share with alkali metals in aqueous solutions?
ⓐ. Formation of hydroxides directly.
ⓑ. Formation of hydrides by accepting electrons.
ⓒ. Ability to displace metals from their salts.
ⓓ. Formation of cations in acid medium.
Correct Answer: Formation of cations in acid medium.
Explanation: In aqueous acids, hydrogen forms $H^+$ ions, similar to the cations ($Na^+$, $K^+$) formed by alkali metals. These ions are responsible for the characteristic conductivity and reactivity in aqueous solutions.
20. Why is hydrogen sometimes grouped with alkali metals in periodic table discussions?
ⓐ. It is metallic in nature.
ⓑ. It has the same melting point as sodium.
ⓒ. It has one valence electron in its outermost shell.
ⓓ. It forms diatomic molecules like metals.
Correct Answer: It has one valence electron in its outermost shell.
Explanation: The $1s^1$ configuration of hydrogen is analogous to the $ns^1$ configuration of alkali metals. This similarity in outer-shell structure explains many of their shared chemical properties, though hydrogen remains a non-metal under normal conditions.
21. In what way does hydrogen resemble halogens?
ⓐ. Both have one electron in their outermost shell.
ⓑ. Both have two electrons in their outermost shell.
ⓒ. Both have metallic properties.
ⓓ. Both form cations easily.
Correct Answer: Both have one electron in their outermost shell.
Explanation: Hydrogen has the configuration $1s^1$, while halogens have $ns^2np^5$. Both need one electron to attain the next noble gas configuration — $H$ to form $H^-$ and halogens to form $X^-$. Hence, they exhibit a similar tendency to gain one electron.
22. Hydrogen resembles halogens because it:
ⓐ. Exists in the monoatomic form.
ⓑ. Exists as a diatomic molecule.
ⓒ. Forms basic oxides.
ⓓ. Shows metallic conductivity.
Correct Answer: Exists as a diatomic molecule.
Explanation: Hydrogen forms the molecule $H_2$, similar to halogens that form diatomic molecules like $F_2$, $Cl_2$, $Br_2$, and $I_2$. This molecular form is due to the covalent bond between identical atoms, showing strong resemblance in molecular structure.
23. Which compound of hydrogen is similar to hydrogen halides in structure?
ⓐ. $NH_3$
ⓑ. $H_2O$
ⓒ. $H_2S$
ⓓ. $HCl$
Correct Answer: $HCl$
Explanation: Hydrogen chloride ($HCl$) is a covalent compound formed by sharing one electron between hydrogen and chlorine, similar to how halogens form compounds with hydrogen. These compounds are volatile and ionize in water to produce acids.
24. Which of the following represents the similarity in electron gain behavior of hydrogen and halogens?
ⓐ. $H \rightarrow H^+ + e^-$
ⓑ. $H + e^- \rightarrow H^-$
ⓒ. $Cl \rightarrow Cl^+ + e^-$
ⓓ. $Na \rightarrow Na^+ + e^-$
Correct Answer: $H + e^- \rightarrow H^-$
Explanation: Hydrogen, like halogens, can gain one electron to achieve a stable configuration. The reaction $H + e^- \rightarrow H^-$ forms the hydride ion, just as $Cl + e^- \rightarrow Cl^-$ forms a chloride ion. This electron gain tendency shows their resemblance.
25. Both hydrogen and halogens:
ⓐ. Have high electropositivity.
ⓑ. Form univalent ions.
ⓒ. Are good conductors of electricity.
ⓓ. Readily form metallic bonds.
Correct Answer: Form univalent ions.
Explanation: Hydrogen forms $H^+$ or $H^-$ ions depending on the reaction, while halogens typically form $X^-$ ions. The univalency of both elements arises from their need to attain stable noble gas configurations.
26. Hydrogen resembles halogens in which of the following reactions?
ⓐ. Formation of $HCl$
ⓑ. Formation of $H_2O$
ⓒ. Reaction with metals to form hydrides
ⓓ. Reaction with acids to produce hydrogen gas
Correct Answer: Reaction with metals to form hydrides
Explanation: Hydrogen reacts with metals like sodium and calcium to form ionic hydrides ($NaH$, $CaH_2$). Similarly, halogens react with metals to form ionic halides ($NaCl$, $CaCl_2$). Both involve electron gain by non-metal (hydrogen or halogen).
27. What is the key difference between hydrogen and halogens despite their resemblance?
ⓐ. Hydrogen can lose or gain an electron, while halogens only gain.
ⓑ. Hydrogen is a solid, while halogens are gases.
ⓒ. Hydrogen always forms anions.
ⓓ. Hydrogen has more electrons than halogens.
Correct Answer: Hydrogen can lose or gain an electron, while halogens only gain.
Explanation: Hydrogen shows dual nature — it can lose one electron to form $H^+$ (like alkali metals) or gain one to form $H^-$ (like halogens). Halogens, on the other hand, typically gain electrons to form negatively charged ions ($X^-$).
28. Hydrogen and halogens both form volatile covalent compounds because:
ⓐ. They have low electronegativity.
ⓑ. They can form single covalent bonds.
ⓒ. They are heavy elements.
ⓓ. They are metals.
Correct Answer: They can form single covalent bonds.
Explanation: Hydrogen ($H_2$) and halogens ($Cl_2$, $Br_2$) both form covalent bonds by sharing one electron each. The resulting molecules are light and volatile gases. Their covalent nature gives them similar bonding characteristics.
29. Which of the following statements about halogen and hydrogen reactivity is correct?
ⓐ. Both are strong oxidising agents.
ⓑ. Both are strong reducing agents.
ⓒ. Both combine with metals to form ionic compounds.
ⓓ. Both form basic oxides.
Correct Answer: Both combine with metals to form ionic compounds.
Explanation: Hydrogen forms ionic hydrides (e.g., $NaH$, $CaH_2$) and halogens form ionic halides (e.g., $NaCl$, $CaCl_2$). In both cases, the metal donates electrons, and the non-metal (H or X) gains electrons to form anions.
30. Which statement correctly describes the bond nature in hydrogen and halogen molecules?
ⓐ. Both contain ionic bonds.
ⓑ. Both contain metallic bonds.
ⓒ. Both contain double covalent bonds.
ⓓ. Both contain single covalent bonds.
Correct Answer: Both contain single covalent bonds.
Explanation: In both $H_2$ and $Cl_2$, each atom shares one electron, forming a single covalent bond. This type of bond ensures molecule stability and demonstrates their resemblance in bonding and molecular structure.
31. Why does hydrogen occupy a unique position in the periodic table?
ⓐ. It resembles only alkali metals.
ⓑ. It resembles only halogens.
ⓒ. It shows similarities with both alkali metals and halogens.
ⓓ. It behaves like a transition element.
Correct Answer: It shows similarities with both alkali metals and halogens.
Explanation: Hydrogen has one electron like alkali metals ($ns^1$) and forms $H^+$ ions. It also resembles halogens in forming diatomic molecules and gaining one electron to form $H^-$. Hence, it cannot be placed definitively in either group, giving it a unique position.
32. Which of the following properties makes hydrogen distinct from all other elements?
ⓐ. It can exist as both $H^+$ and $H^-$ ions.
ⓑ. It always forms ionic compounds.
ⓒ. It has two protons in its nucleus.
ⓓ. It has metallic properties under normal conditions.
Correct Answer: It can exist as both $H^+$ and $H^-$ ions.
Explanation: Hydrogen can lose its single electron to form $H^+$ (like alkali metals) or gain one to form $H^-$ (like halogens). This dual ability to act as both electropositive and electronegative makes hydrogen chemically unique among all elements.
33. Hydrogen cannot be placed in any one group of the periodic table because:
ⓐ. Its ionization enthalpy is very high.
ⓑ. It forms both ionic and covalent compounds.
ⓒ. It shows resemblance to both Group 1 and Group 17 elements.
ⓓ. It does not form diatomic molecules.
Correct Answer: It shows resemblance to both Group 1 and Group 17 elements.
Explanation: The $1s^1$ configuration of hydrogen is similar to $ns^1$ of alkali metals and also allows it to gain one electron like halogens. This dual resemblance creates ambiguity about its correct position in the periodic table.
34. What is the most accepted position of hydrogen in the modern periodic table?
ⓐ. Group 1 only
ⓑ. Group 17 only
ⓒ. Group 2
ⓓ. Placed separately at the top
Correct Answer: Placed separately at the top
Explanation: Due to its dual character, hydrogen is placed separately at the top of the periodic table. This position highlights its unique nature — it can behave both like an alkali metal ($H^+$) and a halogen ($H^-$).
35. Hydrogen differs from alkali metals because:
ⓐ. It is non-metallic and exists as a gas.
ⓑ. It has more than one electron.
ⓒ. It forms solid ionic compounds easily.
ⓓ. It shows variable oxidation states.
Correct Answer: It is non-metallic and exists as a gas.
Explanation: Unlike alkali metals, which are solid, metallic, and conduct electricity, hydrogen is a colorless, odorless gas. Its non-metallic character and molecular form distinguish it from Group 1 elements.
36. Hydrogen differs from halogens because:
ⓐ. It cannot form $H^-$ ions.
ⓑ. It can form both positive and negative ions.
ⓒ. It is diatomic in nature.
ⓓ. It has high electron affinity.
Correct Answer: It can form both positive and negative ions.
Explanation: Halogens form only $X^-$ ions by gaining electrons, whereas hydrogen can form both $H^+$ and $H^-$. This dual ionic behavior makes hydrogen unique and sets it apart from the halogens.
37. Which of the following reasons supports keeping hydrogen separate from all groups?
ⓐ. It exhibits properties of both metals and non-metals.
ⓑ. It forms only covalent compounds.
ⓒ. It exists in a solid state at room temperature.
ⓓ. It has a filled outer shell.
Correct Answer: It exhibits properties of both metals and non-metals.
Explanation: Hydrogen shows metallic properties (forms $H^+$) and non-metallic properties (forms $H^-$, $H_2$). It also reacts with both metals and non-metals. Thus, its ambivalent nature justifies its separate placement in the periodic table.
38. Which statement best explains hydrogen’s intermediate nature?
ⓐ. It shows similarities with both alkali and alkaline earth metals.
ⓑ. It belongs to the transition elements.
ⓒ. It behaves like noble gases.
ⓓ. It shows similarities with both alkali metals and halogens.
Correct Answer: It shows similarities with both alkali metals and halogens.
Explanation: The $1s^1$ configuration of hydrogen is like alkali metals ($ns^1$), but it can also accept an electron to achieve a noble gas configuration, similar to halogens. This dual resemblance makes hydrogen intermediate in character.
39. Hydrogen’s unique placement in the periodic table is primarily due to:
ⓐ. Its high atomic number.
ⓑ. Its single electron and single proton structure.
ⓒ. Its isotopic variety.
ⓓ. Its high molecular mass.
Correct Answer: Its single electron and single proton structure.
Explanation: Hydrogen, with one proton and one electron, is the simplest element. It can behave as a cation or anion, combine covalently or ionically, and exist as atomic or molecular hydrogen. This versatility stems from its simple atomic structure.
40. What conclusion can be drawn about hydrogen’s classification?
ⓐ. It belongs to Group 1 metals.
ⓑ. It belongs to Group 17 halogens.
ⓒ. It has characteristics of both metals and non-metals, so it is placed separately.
ⓓ. It is an inert gas.
Correct Answer: It has characteristics of both metals and non-metals, so it is placed separately.
Explanation: Hydrogen’s ability to form $H^+$ (metal-like) and $H^-$ (non-metal-like) ions makes it impossible to classify strictly as either. Thus, in the modern periodic table, hydrogen is placed at the top, independently of all groups to signify its uniqueness.
41. Which of the following is the most abundant isotope of hydrogen?
ⓐ. Protium ($^1H$)
ⓑ. Deuterium ($^2H$ or $D$)
ⓒ. Tritium ($^3H$ or $T$)
ⓓ. None of these
Correct Answer: Protium ($^1H$)
Explanation: Protium ($^1H$) is the most abundant isotope of hydrogen, constituting about 99.985% of natural hydrogen. It contains one proton and no neutrons in its nucleus. Because of its simplicity, it is the lightest isotope and forms ordinary hydrogen gas ($H_2$).
42. The nucleus of protium consists of:
ⓐ. One proton and one neutron
ⓑ. One neutron only
ⓒ. One proton and two neutrons
ⓓ. One proton only
Correct Answer: One proton only
Explanation: Protium, represented as $^1_1H$, is the simplest atom. It consists of one proton in the nucleus and one electron revolving around it. It has no neutrons, which distinguishes it from deuterium and tritium.
43. Which statement is true about protium ($^1H$)?
ⓐ. It is radioactive.
ⓑ. It is stable and non-radioactive.
ⓒ. It decays into deuterium.
ⓓ. It contains two neutrons.
Correct Answer: It is stable and non-radioactive.
Explanation: Protium is the only stable isotope of hydrogen without any neutrons. Unlike tritium, which is radioactive, protium remains stable indefinitely and is the most common form of hydrogen on Earth.
44. The mass number of protium is:
ⓐ. 0
ⓑ. 1
ⓒ. 2
ⓓ. 3
Correct Answer: 1
Explanation: The mass number of an atom is the sum of protons and neutrons in its nucleus. Protium has one proton and no neutrons, giving it a mass number of 1 ($1 + 0 = 1$). Hence, it is denoted as $^1H$.
45. Which of the following correctly represents protium?
ⓐ. $^2_1H$
ⓑ. $^3_1H$
ⓒ. $^1_0H$
ⓓ. $^1_1H$
Correct Answer: $^1_1H$
Explanation: The notation $^1_1H$ means that protium has one proton (atomic number 1) and one as its mass number, indicating it has no neutrons. This is the most common hydrogen isotope found in nature.
46. Protium combines with oxygen to form:
ⓐ. Heavy water ($D_2O$)
ⓑ. Hydrogen peroxide ($H_2O_2$)
ⓒ. Ordinary water ($H_2O$)
ⓓ. Ozone ($O_3$)
Correct Answer: Ordinary water ($H_2O$)
Explanation: When protium ($^1H$) reacts with oxygen, it forms ordinary water:
$2H_2 + O_2 \rightarrow 2H_2O$.
In contrast, deuterium forms heavy water ($D_2O$). Thus, the common water we drink mainly contains protium.
47. Which isotope of hydrogen does NOT contain any neutron?
ⓐ. Deuterium
ⓑ. Tritium
ⓒ. Protium
ⓓ. All contain one neutron
Correct Answer: Protium
Explanation: The protium nucleus contains only one proton and no neutrons. Deuterium contains one neutron, while tritium has two. Therefore, protium is the only hydrogen isotope without any neutrons.
48. What is the relative atomic mass of protium?
ⓐ. 2.014
ⓑ. 1.000
ⓒ. 3.016
ⓓ. 1.008
Correct Answer: 1.008
Explanation: The actual, precisely measured relative atomic mass of a neutral protium atom is about 1.007825 amu (or Da, Daltons). This value is slightly greater than 1 due to contributions from the electron mass and the mass defect (binding energy) effects when compared to the carbon-12 standard.
49. Protium forms a covalent bond in $H_2$ molecule by:
ⓐ. Transfer of one electron
ⓑ. Sharing of one electron between two atoms
ⓒ. Gaining two electrons from oxygen
ⓓ. Donating two electrons to chlorine
Correct Answer: Sharing of one electron between two atoms
Explanation: In a dihydrogen molecule ($H_2$), each hydrogen atom shares one electron to form a single covalent bond. The resulting molecule achieves the stable electronic configuration of helium ($1s^2$).
50. Why is protium considered chemically more reactive than deuterium?
ⓐ. It has a larger atomic mass.
ⓑ. It has a higher bond dissociation energy.
ⓒ. It has a smaller mass and forms bonds more easily.
ⓓ. It is radioactive in nature.
Correct Answer: It has a smaller mass and forms bonds more easily.
Explanation: Protium, being lighter, moves faster and has lower bond dissociation energy than deuterium. This makes chemical reactions involving protium occur faster. Thus, protium is more reactive in many hydrogen-based reactions compared to deuterium.
51. Which of the following symbols represents deuterium correctly?
ⓐ. $^1_1H$
ⓑ. $^2_1H$ or $D$
ⓒ. $^3_1H$ or $T$
ⓓ. $^2_0H$
Correct Answer: $^2_1H$ or $D$
Explanation: Deuterium, also known as heavy hydrogen, is represented as $^2_1H$ or simply $D$. It contains one proton and one neutron in its nucleus, giving it a mass number of 2. The presence of one neutron makes it heavier than protium.
52. What is the percentage abundance of deuterium in natural hydrogen?
ⓐ. 0.015%
ⓑ. 99.985%
ⓒ. 1.50%
ⓓ. 0.15%
Correct Answer: 0.015%
Explanation: Deuterium makes up about 0.015% of naturally occurring hydrogen. Though it is much less abundant than protium, its chemical behavior is quite similar, with only slight differences due to its greater mass.
53. The nucleus of deuterium contains:
ⓐ. One proton only
ⓑ. Two protons and one neutron
ⓒ. One proton and two neutrons
ⓓ. One proton and one neutron
Correct Answer: One proton and one neutron
Explanation: Deuterium ($^2_1H$) consists of one proton and one neutron in the nucleus, making its mass number 2. The presence of a neutron increases its mass compared to protium, which lacks a neutron.
54. The molecular formula of heavy hydrogen gas is:
ⓐ. $H_2$
ⓑ. $D_2$
ⓒ. $HD$
ⓓ. $D_2O$
Correct Answer: $D_2$
Explanation: Heavy hydrogen gas, also known as deuterium gas, exists as a diatomic molecule ($D_2$). It behaves chemically like hydrogen gas but is denser because each atom contains an additional neutron.
55. When deuterium reacts with oxygen, the product formed is:
ⓐ. Ordinary water ($H_2O$)
ⓑ. Hydrogen peroxide ($H_2O_2$)
ⓒ. Heavy water ($D_2O$)
ⓓ. Deuterium oxide ($D_2O_2$)
Correct Answer: Heavy water ($D_2O$)
Explanation: Deuterium reacts with oxygen to form heavy water ($D_2O$):
$2D_2 + O_2 \rightarrow 2D_2O$.
Heavy water is denser than ordinary water ($H_2O$) and is widely used as a moderator in nuclear reactors.
56. The boiling point of heavy water ($D_2O$) compared to ordinary water ($H_2O$) is:
ⓐ. Lower
ⓑ. Zero
ⓒ. Same
ⓓ. Higher
Correct Answer: Higher
Explanation: The boiling point of heavy water is $101.4^\circ C$, slightly higher than that of ordinary water ($100^\circ C$). The higher mass of deuterium and stronger $D–O$ bond increase intermolecular forces, raising the boiling point.
57. Which of the following statements about deuterium is true?
ⓐ. It is radioactive.
ⓑ. It is stable and non-radioactive.
ⓒ. It decays into tritium.
ⓓ. It is found only in laboratories.
Correct Answer: It is stable and non-radioactive.
Explanation: Deuterium is a stable isotope of hydrogen containing one neutron. Unlike tritium, it does not undergo radioactive decay. It occurs naturally in water and has similar chemical properties to protium.
58. Which compound is formed when deuterium reacts with chlorine?
ⓐ. $DCl$
ⓑ. $HCl$
ⓒ. $D_2Cl_2$
ⓓ. $H_2Cl_2$
Correct Answer: $DCl$
Explanation: Deuterium reacts with chlorine to form deuterium chloride ($DCl$):
$D_2 + Cl_2 \rightarrow 2DCl$.
This is analogous to the reaction of hydrogen with chlorine, but $DCl$ is heavier due to the presence of deuterium.
59. What is the main use of deuterium in nuclear reactors?
ⓐ. As a fuel
ⓑ. As a coolant
ⓒ. As a neutron moderator
ⓓ. As a reducing agent
Correct Answer: As a neutron moderator
Explanation: Deuterium, in the form of heavy water ($D_2O$), slows down fast neutrons in nuclear reactors, increasing the probability of fission. It moderates the speed of neutrons without capturing them easily, ensuring controlled chain reactions.
60. Why do reactions involving deuterium occur more slowly than those with protium?
ⓐ. Deuterium has a smaller atomic mass.
ⓑ. Deuterium forms stronger bonds than protium.
ⓒ. Deuterium is radioactive.
ⓓ. Deuterium is metallic in nature.
Correct Answer: Deuterium forms stronger bonds than protium.
Explanation: The bond dissociation energy of a $D–X$ bond (where X is another atom) is greater than that of an $H–X$ bond because of the higher mass of deuterium. This leads to slower reaction rates, known as the isotope effect, observed in chemical and biological systems.
61. Which of the following symbols represents tritium correctly?
ⓐ. $^1_1H$
ⓑ. $^2_1H$
ⓒ. $^4_1H$
ⓓ. $^3_1H$ or $T$
Correct Answer: $^3_1H$ or $T$
Explanation: Tritium is the radioactive isotope of hydrogen and is represented as $^3_1H$ or simply $T$. It contains one proton and two neutrons in its nucleus, giving it a mass number of 3. The presence of extra neutrons makes it unstable, and it undergoes beta decay to form helium-3. Because of this radioactive nature, tritium is rare in nature and must often be produced artificially.
62. How many neutrons are present in tritium?
ⓐ. None
ⓑ. One
ⓒ. Two
ⓓ. Three
Correct Answer: Two
Explanation: Tritium ($^3_1H$) has a mass number of 3 and an atomic number of 1. The number of neutrons is obtained by subtracting atomic number from mass number: $3 – 1 = 2$. Thus, tritium has one proton, two neutrons, and one electron. This extra neutron count makes tritium heavier and radioactive compared to protium and deuterium.
63. Tritium undergoes radioactive decay to form which element?
ⓐ. Deuterium ($^2H$)
ⓑ. Helium-3 ($^3_2He$)
ⓒ. Hydrogen-2 ($^2_1H$)
ⓓ. Lithium ($^3_3Li$)
Correct Answer: Helium-3 ($^3_2He$)
Explanation: Tritium decays by emitting a beta particle ($\beta^-$) and transforms into helium-3:
$$^3_1H \rightarrow ^3_2He + \beta^- + \bar{\nu}$$
In this process, one neutron is converted into a proton, increasing the atomic number from 1 to 2. This type of decay is known as beta decay, and the resulting helium-3 is a stable isotope of helium.
64. The half-life of tritium is approximately:
ⓐ. 12.3 years
ⓑ. 10 days
ⓒ. 3.5 hours
ⓓ. 100 years
Correct Answer: 12.3 years
Explanation: Tritium has a half-life of about 12.3 years, meaning half of a given amount decays during this time. This makes it moderately long-lived compared to other radioactive isotopes. Its controlled beta decay without gamma radiation makes it useful for applications like luminous watches, exit signs, and as a tracer in scientific research.
65. Which statement about tritium is true?
ⓐ. It is stable and non-radioactive.
ⓑ. It emits alpha particles on decay.
ⓒ. It emits beta particles on decay.
ⓓ. It forms helium-4 upon decay.
Correct Answer: It emits beta particles on decay.
Explanation: Tritium decays by emitting a low-energy beta particle ($\beta^-$) and an antineutrino, converting a neutron into a proton. The product of this decay is helium-3. Since the emitted beta radiation is weak, tritium is not highly dangerous externally but can be harmful if inhaled or ingested.
66. Tritium can be artificially produced by:
ⓐ. Electrolysis of water
ⓑ. Nuclear reaction of lithium with neutrons
ⓒ. Decomposition of ammonia
ⓓ. Reaction of hydrogen with chlorine
Correct Answer: Nuclear reaction of lithium with neutrons
Explanation: Tritium is produced artificially in nuclear reactors when lithium absorbs neutrons:
$$^6_3Li + n \rightarrow ^3_1H + ^4_2He$$
This controlled process produces tritium used in nuclear fusion research and luminous devices. Natural tritium is also formed in the upper atmosphere due to cosmic ray interactions with nitrogen.
67. In nature, tritium is formed mainly by:
ⓐ. Volcanic activity
ⓑ. Lightning reactions
ⓒ. Cosmic ray interactions with atmospheric gases
ⓓ. Radioactive decay of uranium
Correct Answer: Cosmic ray interactions with atmospheric gases
Explanation: When high-energy cosmic rays strike nitrogen in the upper atmosphere, tritium is produced through nuclear reactions like:
$$^{14}N + n \rightarrow ^{12}C + ^3H$$
The tritium thus formed mixes with atmospheric water and falls to Earth as tritiated water ($HTO$). However, this natural amount is extremely small, making tritium one of the rarest hydrogen isotopes on Earth.
68. Which of the following best describes tritium’s role in nuclear fusion?
ⓐ. It reacts with deuterium to produce large amounts of energy.
ⓑ. It absorbs neutrons and forms helium.
ⓒ. It acts as a catalyst in fusion reactions.
ⓓ. It slows down neutrons in fission reactions.
Correct Answer: It reacts with deuterium to produce large amounts of energy.
Explanation: Tritium is a crucial fuel in nuclear fusion reactions. When combined with deuterium, it forms helium and releases a massive amount of energy:
$$^2_1H + ^3_1H \rightarrow ^4_2He + n + 17.6\text{ MeV}$$
This reaction forms the basis of hydrogen bomb technology and is also studied for clean energy production in fusion reactors like ITER.
69. The radioactive nature of tritium is primarily due to:
ⓐ. Its unstable proton
ⓑ. Its metallic bonding nature
ⓒ. The presence of too many electrons
ⓓ. The excess of neutrons in its nucleus
Correct Answer: The excess of neutrons in its nucleus
Explanation: Tritium’s nucleus has one proton and two neutrons, making it neutron-rich. This imbalance leads to instability, causing one neutron to convert into a proton via beta decay. The emission of beta radiation helps the atom achieve a more stable proton-to-neutron ratio, forming stable helium-3.
70. Which of the following statements about tritium water ($T_2O$) is correct?
ⓐ. It is stable and non-radioactive.
ⓑ. It glows naturally and is highly radioactive.
ⓒ. It has the same density as ordinary water.
ⓓ. It contains no hydrogen atoms.
Correct Answer: It glows naturally and is highly radioactive.
Explanation: Tritium oxide ($T_2O$), or tritiated water, is radioactive because it contains tritium atoms that emit beta radiation. The decay of tritium inside water molecules can cause slight luminescence. It is used in scientific research as a tracer and in self-luminous devices like watch dials and emergency exit signs. However, it must be handled with care due to its internal radiation hazards.
71. Which of the following statements correctly describes the isotopes of hydrogen?
ⓐ. They have different atomic numbers and same mass numbers.
ⓑ. They have same atomic number but different mass numbers.
ⓒ. They have same number of neutrons.
ⓓ. They have different electronic configurations.
Correct Answer: They have same atomic number but different mass numbers.
Explanation: All isotopes of hydrogen (protium $^1H$, deuterium $^2H$, and tritium $^3H$) have one proton and one electron, giving them the same atomic number (1). However, they differ in the number of neutrons (0, 1, and 2 respectively), which causes their mass numbers to differ (1, 2, and 3). This difference in mass leads to slight variations in their physical properties while maintaining similar chemical behavior.
72. Which of the following hydrogen isotopes is radioactive?
ⓐ. Protium ($^1H$)
ⓑ. Deuterium ($^2H$)
ⓒ. Tritium ($^3H$)
ⓓ. All are radioactive
Correct Answer: Tritium ($^3H$)
Explanation: Tritium is the only radioactive isotope of hydrogen, containing one proton and two neutrons. Its unstable nucleus decays through beta emission, converting one neutron into a proton and forming helium-3. The half-life of tritium is about 12.3 years. In contrast, protium and deuterium are stable isotopes that do not undergo radioactive decay.
73. The chemical properties of hydrogen isotopes are similar because:
ⓐ. They have the same number of neutrons.
ⓑ. They have identical electronic configurations.
ⓒ. Their nuclei contain the same number of neutrons.
ⓓ. They have different atomic numbers.
Correct Answer: They have identical electronic configurations.
Explanation: The chemical behavior of an element depends on its electron configuration, not on its mass or number of neutrons. All three isotopes of hydrogen have one electron in the 1s orbital. Hence, they exhibit nearly identical chemical properties, though reaction rates may vary slightly due to mass differences (the isotope effect).
74. Which physical property of hydrogen isotopes is different?
ⓐ. Color and odor
ⓑ. Chemical reactivity
ⓒ. Valency
ⓓ. Density and boiling point
Correct Answer: Density and boiling point
Explanation: The physical properties such as density, boiling point, and melting point vary among hydrogen isotopes because these properties depend on atomic mass. For instance, heavy water ($D_2O$) has higher boiling and melting points than ordinary water ($H_2O$) due to stronger $D–O$ bonds. These differences are important in isotope separation and research applications.
75. Heavy water differs from ordinary water because:
ⓐ. It is more volatile.
ⓑ. It has a lower boiling point.
ⓒ. It is denser and has a higher boiling point.
ⓓ. It freezes at a lower temperature.
Correct Answer: It is denser and has a higher boiling point.
Explanation: Heavy water ($D_2O$) is denser (1.105 g/cm³) and has a higher boiling point (101.4°C) and melting point (3.8°C) than ordinary water ($H_2O$). This is due to the higher mass of deuterium compared to protium. These properties make heavy water useful as a moderator in nuclear reactors to slow down fast neutrons and sustain controlled fission reactions.
76. Which isotope of hydrogen is used as a tracer in biochemical and environmental studies?
ⓐ. Protium
ⓑ. Deuterium
ⓒ. Tritium
ⓓ. Both B and C
Correct Answer: Both B and C
Explanation: Deuterium ($^2H$) and tritium ($^3H$) are widely used as tracers to study chemical, biological, and environmental processes. Deuterium, being stable and non-radioactive, is used in metabolic and reaction pathway studies, while tritium, being radioactive, is used for tracing the movement of water or biological molecules due to its measurable beta emission.
77. Why is tritium useful in self-luminous devices like watch dials and exit signs?
ⓐ. It emits strong gamma radiation.
ⓑ. It glows when it reacts with air.
ⓒ. It emits low-energy beta radiation that excites phosphors to glow.
ⓓ. It produces light through fusion.
Correct Answer: It emits low-energy beta radiation that excites phosphors to glow.
Explanation: Tritium’s low-energy beta particles cannot penetrate glass or human skin but can excite phosphorescent materials, producing continuous light without electricity. This property is used in luminous watches, aircraft dials, and emergency exit signs. The radiation is safe under controlled conditions as it poses minimal external hazard.
78. Which hydrogen isotope is used in nuclear fusion reactions to produce energy?
ⓐ. Deuterium and tritium
ⓑ. Protium
ⓒ. Deuterium only
ⓓ. Tritium only
Correct Answer: Deuterium and tritium
Explanation: The most promising nuclear fusion reaction combines deuterium ($^2H$) and tritium ($^3H$) to form helium and release tremendous energy: $^2_1H + ^3_1H \rightarrow ^4_2He + n + 17.6 \text{ MeV}$. This reaction forms the basis for potential clean energy generation in fusion reactors and occurs naturally in the sun, where hydrogen isotopes fuse under extreme temperatures and pressures.
79. Which property of isotopes makes them useful in research and medical fields?
ⓐ. Their chemical reactivity
ⓑ. Their non-metallic nature
ⓒ. Their different atomic numbers
ⓓ. Their identical atomic numbers but different masses
Correct Answer: Their identical atomic numbers but different masses
Explanation: Isotopes of an element behave chemically the same but can be distinguished physically due to mass differences. This property allows scientists to use stable isotopes like deuterium as tracers in metabolic studies and radioactive isotopes like tritium in radiolabeling experiments, radiation therapy, and environmental tracking.
80. Why are the reaction rates of deuterium compounds slower than those of protium compounds?
ⓐ. Deuterium is less stable.
ⓑ. Deuterium has a higher bond energy and greater mass.
ⓒ. Deuterium has more electrons.
ⓓ. Deuterium reacts only with metals.
Correct Answer: Deuterium has a higher bond energy and greater mass.
Explanation: The heavier mass of deuterium results in stronger bonds such as D–O and D–Cl compared to H–O and H–Cl. These stronger bonds require more energy to break, slowing down reaction rates. This difference in rate due to isotope mass is known as the isotope effect, a principle used to study reaction mechanisms and biological processes.
81. Which of the following correctly describes dihydrogen under normal conditions?
ⓐ. Colourless, odourless, tasteless gas
ⓑ. Greenish, pungent-smelling gas
ⓒ. Bluish, poisonous gas
ⓓ. Colourless liquid
Correct Answer: Colourless, odourless, tasteless gas
Explanation: Dihydrogen ($H_2$) is a colourless, odourless, and tasteless gas at room temperature. It is non-toxic and non-corrosive but extremely light and highly combustible. Because of its low molecular weight (2.016 u), it diffuses rapidly and escapes easily from containers if not properly sealed.
82. Which statement about the solubility of dihydrogen in water is correct?
ⓐ. It is highly soluble in water.
ⓑ. It is moderately soluble in water.
ⓒ. It is sparingly soluble in water.
ⓓ. It does not dissolve in water at all.
Correct Answer: It is sparingly soluble in water.
Explanation: Dihydrogen has very low solubility in water — about 0.00016 g per 100 mL at 20°C. This is due to its non-polar nature and weak interaction with polar water molecules. However, this small solubility is sufficient for biological and industrial processes involving hydrogen gas.
83. What is the density of dihydrogen gas at standard temperature and pressure (STP)?
ⓐ. 0.0899 g/L
ⓑ. 1.29 g/L
ⓒ. 0.45 g/L
ⓓ. 2.016 g/L
Correct Answer: 0.0899 g/L
Explanation: At STP (0°C and 1 atm), the density of dihydrogen is 0.0899 g/L, making it the lightest gas known. Its extremely low density enables it to rise quickly in the atmosphere and makes it useful in lighter-than-air applications such as weather balloons and airships (though flammability limits its use today).
84. The boiling point of dihydrogen is approximately:
ⓐ. 0°C
ⓑ. –196°C
ⓒ. –100°C
ⓓ. –252.87°C
Correct Answer: –252.87°C
Explanation: Dihydrogen has a boiling point of –252.87°C (20.28 K) due to weak van der Waals forces between its molecules. The low molecular mass and non-polar character prevent strong intermolecular attractions, which is why hydrogen remains gaseous under ordinary conditions and liquefies only at extremely low temperatures.
85. The melting point of dihydrogen is approximately:
ⓐ. –273°C
ⓑ. –259.14°C
ⓒ. –200°C
ⓓ. –100°C
Correct Answer: –259.14°C
Explanation: The melting point of dihydrogen is very low (–259.14°C or 14.01 K) because of weak intermolecular forces. These very low melting and boiling points classify hydrogen as a cryogenic substance, which requires special insulated storage containers called Dewar flasks when handled in liquid form.
86. Dihydrogen gas is lighter than air because:
ⓐ. It reacts with oxygen in air.
ⓑ. It has a lower molecular weight than air.
ⓒ. It dissolves completely in air.
ⓓ. It condenses easily at room temperature.
Correct Answer: It has a lower molecular weight than air.
Explanation: The molecular weight of $H_2$ is 2.016, while the average molecular weight of air is about 29. As a result, hydrogen is about 14.5 times lighter than air. This property once made it useful in airships and weather balloons, though it was later replaced by non-flammable helium due to hydrogen’s explosive nature.
87. The critical temperature of dihydrogen is:
ⓐ. 33 K
ⓑ. 20.28 K
ⓒ. 5.4 K
ⓓ. 12.8 K
Correct Answer: 12.8 K
Explanation: The critical temperature of a gas is the highest temperature at which it can be liquefied by pressure. For dihydrogen, this value is very low (12.8 K), indicating that it cannot be easily liquefied by compression at room temperature. Special cryogenic cooling methods are required to convert it into liquid hydrogen.
88. Which of the following statements is correct regarding the diffusibility of dihydrogen?
ⓐ. It diffuses slower than air.
ⓑ. It diffuses only in vacuum.
ⓒ. It does not diffuse at all.
ⓓ. It diffuses faster than air.
Correct Answer: It diffuses faster than air.
Explanation: The rate of diffusion of a gas is inversely proportional to the square root of its molecular mass (Graham’s law). Because hydrogen’s molecular mass (2.016) is much lower than that of air (~29), hydrogen diffuses about four times faster than air. This property makes it useful in chemical reactions requiring rapid mixing but also increases explosion risks in open environments.
89. The specific heat of dihydrogen gas is:
ⓐ. Very high
ⓑ. Very low
ⓒ. Equal to oxygen
ⓓ. Same as nitrogen
Correct Answer: Very high
Explanation: Dihydrogen has a very high specific heat capacity (14.32 J/g·K), which means it can absorb large amounts of heat energy with only a small rise in temperature. This property makes it valuable as a cooling agent and as a potential energy carrier in advanced fuel and refrigeration systems.
90. Which statement is true about the flammability of dihydrogen gas?
ⓐ. It does not burn in air.
ⓑ. It burns with a pale blue flame forming water.
ⓒ. It burns with a yellow smoky flame producing soot.
ⓓ. It is completely inert to oxygen.
Correct Answer: It burns with a pale blue flame forming water.
Explanation: Dihydrogen is highly flammable and burns in oxygen with a nearly invisible pale blue flame to form water vapor according to the reaction $2H_2 + O_2 \rightarrow 2H_2O$. The combustion is exothermic, releasing about 286 kJ/mol of energy. This high energy release makes hydrogen an efficient fuel, though safety measures are essential due to its explosive potential when mixed with air.
91. Which of the following reactions correctly represents the combustion of dihydrogen in oxygen?
ⓐ. $H_2 + O_2 \rightarrow 2H_2O_2$
ⓑ. $2H_2 + O_2 \rightarrow 2H_2O$
ⓒ. $H_2 + O_2 \rightarrow H_2O$
ⓓ. $H_2 + 2O_2 \rightarrow 2H_2O$
Correct Answer: $2H_2 + O_2 \rightarrow 2H_2O$
Explanation: Dihydrogen burns in oxygen with a pale blue flame to form water vapor. The reaction is highly exothermic and releases about 286 kJ/mol of energy. Because of this large energy release, hydrogen is used as a rocket fuel. However, the mixture of hydrogen and oxygen in a confined space can cause explosions, known as oxyhydrogen explosions.
92. When hydrogen reacts with chlorine in the presence of sunlight, the main product is:
ⓐ. $HCl$
ⓑ. $Cl_2O$
ⓒ. $HClO$
ⓓ. $HClO_3$
Correct Answer: $HCl$
Explanation: Dihydrogen reacts explosively with chlorine in sunlight to form hydrogen chloride gas according to $H_2 + Cl_2 \xrightarrow{h\nu} 2HCl$. The reaction proceeds via a chain mechanism involving free radicals. In diffused light, the reaction is slower, while in the dark, it does not occur. This demonstrates hydrogen’s strong affinity for halogens.
93. Which of the following halogens reacts most vigorously with hydrogen?
ⓐ. Iodine
ⓑ. Chlorine
ⓒ. Bromine
ⓓ. Fluorine
Correct Answer: Fluorine
Explanation: Fluorine is the most reactive halogen and reacts explosively with hydrogen even in the dark at low temperatures to form hydrogen fluoride ($HF$): $H_2 + F_2 \rightarrow 2HF$. Chlorine reacts in sunlight, bromine requires heating, and iodine reacts only on heating and in the presence of a catalyst. The reactivity decreases from fluorine to iodine.
94. Hydrogen reacts with nitrogen to form ammonia in the presence of a catalyst. This process is called:
ⓐ. Haber’s process
ⓑ. Ostwald process
ⓒ. Contact process
ⓓ. Bosch process
Correct Answer: Haber’s process
Explanation: Ammonia is synthesized industrially by the Haber process: $N_2 + 3H_2 \rightleftharpoons 2NH_3; \Delta H = -92.4,\text{kJ/mol}$. The reaction is carried out at 450–500°C, 200–300 atm, and in the presence of iron catalyst with molybdenum as promoter. The process is exothermic and reversible, so moderate temperature and high pressure favor ammonia formation.
95. Which of the following equations represents the reaction between hydrogen and sulfur?
ⓐ. $H_2 + S \rightarrow H_2S$
ⓑ. $H_2 + S_2 \rightarrow 2HS$
ⓒ. $2H_2 + S \rightarrow H_4S$
ⓓ. $H_2 + 2S \rightarrow H_2S_2$
Correct Answer: $H_2 + S \rightarrow H_2S$
Explanation: When hydrogen reacts with sulfur vapors at around 300°C, hydrogen sulfide gas ($H_2S$) is formed. The gas has a characteristic rotten egg smell and is highly toxic. This reaction demonstrates hydrogen’s reducing ability and tendency to form covalent hydrides with non-metals.
96. Hydrogen reacts with metals like sodium to form:
ⓐ. Metal halides
ⓑ. Metal oxides
ⓒ. Metal hydrides
ⓓ. Metal hydroxides
Correct Answer: Metal hydrides
Explanation: Hydrogen reacts with highly electropositive metals such as sodium, potassium, and calcium to form ionic hydrides. For example, $2Na + H_2 \rightarrow 2NaH$. In these compounds, hydrogen exists as $H^-$ ion. These hydrides react with water to release hydrogen gas, making them powerful reducing agents.
97. Which of the following metals does not react directly with hydrogen to form a hydride?
ⓐ. Sodium
ⓑ. Calcium
ⓒ. Lithium
ⓓ. Copper
Correct Answer: Copper
Explanation: Only highly electropositive metals (alkali and alkaline earth metals) react directly with hydrogen to form ionic hydrides. Transition metals like copper, silver, and gold do not form stable hydrides because their metallic bonds are stronger and their affinity for hydrogen is very low.
98. Which of the following reactions shows the reducing property of hydrogen?
ⓐ. $H_2 + Cl_2 \rightarrow 2HCl$
ⓑ. $CuO + H_2 \rightarrow Cu + H_2O$
ⓒ. $H_2 + O_2 \rightarrow H_2O$
ⓓ. $N_2 + 3H_2 \rightarrow 2NH_3$
Correct Answer: $CuO + H_2 \rightarrow Cu + H_2O$
Explanation: Hydrogen acts as a strong reducing agent at high temperatures. It reduces metal oxides such as $CuO$, $Fe_2O_3$, and $PbO$ to metals. The reaction $CuO + H_2 \rightarrow Cu + H_2O$ shows hydrogen’s ability to donate electrons and convert the oxide back into its metallic form, producing water as a byproduct.
99. Dihydrogen reacts with carbon monoxide in the presence of a catalyst to form methanol. This process is known as:
ⓐ. Haber process
ⓑ. Bosch process
ⓒ. Fischer–Tropsch process
ⓓ. Bergius process
Correct Answer: Fischer–Tropsch process
Explanation: In the Fischer–Tropsch process, a mixture of carbon monoxide and hydrogen, known as synthesis gas or syngas, reacts over cobalt or iron catalysts to form methanol and hydrocarbons: $CO + 2H_2 \rightarrow CH_3OH$. This process converts syngas derived from coal or natural gas into useful liquid fuels, making it a cornerstone of industrial chemistry.
100. Hydrogen reacts with unsaturated hydrocarbons in the presence of catalysts like Ni or Pt to produce:
ⓐ. Alcohols
ⓑ. Alkanes
ⓒ. Aldehydes
ⓓ. Ketones
Correct Answer: Alkanes
Explanation: The addition of hydrogen to unsaturated hydrocarbons (alkenes or alkynes) in the presence of catalysts such as nickel, platinum, or palladium is called hydrogenation. For example, $C_2H_4 + H_2 \xrightarrow{Ni} C_2H_6$. This reaction converts vegetable oils into solid fats (e.g., margarine production) and is widely used in the food and petrochemical industries due to its economic and practical importance.
Welcome to Class 11 Chemistry MCQs – Chapter 9: Hydrogen (Part of 4). This chapter explores the fascinating world of hydrogen, a key element in both organic and inorganic chemistry. Hydrogen plays a critical role in chemical reactions, industrial applications, and biological processes. This page offers 100 MCQs with detailed explanations to help you gain a deep understanding of hydrogen’s properties, reactions, and uses. These MCQs are designed to sharpen your exam skills for Board exams, JEE, NEET, and other competitive tests.
Navigation & parts: This chapter contains 343 MCQs divided into 4 parts (100 + 100 + 100 + 43). This page presents the first set of 100 MCQs with answers and explanations. Use the Part buttons above to continue to the next sections.
What you will learn & practice (Chapter 9: Hydrogen)
- Occurrence of hydrogen: natural sources, production methods like electrolysis, water gas shift reaction
- Isotopes of hydrogen: protium, deuterium, tritium and their significance in chemistry and industry
- Hydrogen as a reducing agent in various reactions including reduction of metals and organic compounds
- Hydrogen in the form of hydrides: metal hydrides, molecular hydrides, and their uses in chemical synthesis
- Hydrogenation in industry, especially in the production of vegetable oils and fuels
- Water: its properties and importance, structure, and its role in biological processes and industrial applications
- Hydrogen bonds: the significance of hydrogen bonding in water and other compounds like alcohols and acids
- Applications of hydrogen: fuel cells, hydrogen storage, and its role in rocket propulsion and the chemical industry
- Important reactions involving hydrogen: examples from the preparation of hydrogen, oxidation reactions, and combustion of hydrogen
- Hydrogen in acids and bases: the role of hydrogen ions (protons) in acid-base reactions and their applications in buffer systems
How to use this site to master Hydrogen MCQs
- Warm-up (10 mins): Skim through the topics above and keep a formula sheet ready (hydride, hydrogenation, isotope usage).
- Active attempt: Solve 10–20 MCQs at a time. Check your answer immediately and read the explanation carefully.
- Mark tricky questions: Use the ❤️ Heart to tag difficult questions. Use the Favourite Toggle above to filter and revisit them anytime.
- Workspace feature: Under each question, click Workspace to write your thoughts, notes, or important tricks. These will auto-save and be available whenever you need them for future revision.
- Smart revision: Use the Random button to challenge yourself and avoid learning patterns. For a focused revision, turn on Favourite Toggle.
- Review with intervals: Revisit your Favourite questions in spaced intervals (Day 2, Day 4, and Day 7) to reinforce retention.
Why this helps for Boards, JEE Main & NEET
- Boards: Hydrogen is a fundamental chapter for one-mark questions and conceptual understanding.
- JEE Main/Advanced: Reactions involving hydrogen, such as hydrogenation and hydrogen bonding, are frequently tested in numericals.
- NEET: Conceptual questions on hydrogen isotopes, its reactions, and its role in biological systems are common in NEET.
- Your advantage: With Favourite and Workspace, this chapter is personalized to strengthen weak areas and boost confidence.
Common mistakes to avoid
- Confusing between deuterium and tritium isotopes of hydrogen.
- Forgetting that hydrogen in hydrides can have different oxidation states, affecting reactions.
- Not understanding the mechanism of hydrogenation in industrial applications.
- Overlooking the importance of hydrogen in acid-base chemistry (H+ ions).
- Confusing the terms protium, deuterium, and tritium in reactions.
Progress in hydrogen chemistry comes with practice. Use the ❤️ Heart to save key MCQs, add notes in Workspace, and revise them regularly to retain knowledge. Don’t forget to check back for Part 2 to continue your learning journey!
Explore more: Class 11 Chemistry – Chapter Index, Class 11 – Subject Index, All Classes – MCQ Library.
Quick FAQ
What is hydrogenation?
Hydrogenation is the chemical reaction where hydrogen (H2) is added to a compound, usually in the presence of a catalyst, to reduce or saturate a molecule (e.g., vegetable oils turning into ghee or margarine).
How many MCQs should I do daily?
Start with 30–40 MCQs per day. Ensure that you understand the explanation for each question to gain a deep understanding.
How do I improve my hydrogen MCQ practice?
Revisit your Favourite questions and Workspace notes regularly. Utilize the Random button for a mix of topics and build strong retention.
- 👉 Total MCQs in this chapter: 343 (100 + 100 + 100 + 43)
- 👉 This page: First 100 MCQs with answers & explanations
- 👉 Best for: Boards • JEE/NEET • Hydrogen reactions • concept revision • quick quizzes
- 👉 Next: Use the Part buttons above to continue
FAQs on Hydrogen ▼
▸ What are Hydrogen MCQs in Class 11 Chemistry?
These are multiple-choice questions from Chapter 9 of NCERT Class 11 Chemistry – Hydrogen. They focus on the properties, isotopes, production methods, and applications of hydrogen in various chemical reactions.
▸ How many MCQs are available in this chapter?
There are a total of 343 Hydrogen MCQs. They are divided into 4 structured parts – four sets of 100 questions each, with one set containing 43 questions.
▸ Are Hydrogen MCQs important for JEE and NEET?
Yes, this chapter is essential for JEE and NEET preparation. Key topics like hydrogen bonding, isotopes of hydrogen (deuterium, tritium), and hydrogen’s role in the production of various compounds are commonly tested in competitive exams.
▸ Do these MCQs include correct answers and explanations?
Yes, every MCQ is provided with the correct answer and detailed explanations to help you understand the reasoning behind the solution and reinforce your learning.
▸ Which subtopics are covered in these Hydrogen MCQs?
These MCQs cover subtopics like hydrogen’s occurrence, preparation methods (electrolysis, steam reforming), hydrogen bonding, applications of hydrogen (fuel, reduction reactions), and the properties of hydrogen compounds like hydrides and acids.