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101. What is a fractional oxidation state?
ⓐ. An oxidation state that is a non-integer
ⓑ. The average oxidation state of an element in a compound
ⓒ. The oxidation state of a free element
ⓓ. An oxidation state that is always positive
Correct Answer: An oxidation state that is a non-integer
Explanation: A fractional oxidation state refers to an oxidation number that is a fraction or non-integer, which occurs when an element has an average oxidation state in a compound, often due to resonance or the presence of multiple oxidation states in a molecule or complex.
102. Which of the following compounds contains an element with a fractional oxidation state?
ⓐ. $NaCl$
ⓑ. $CuSO_4$
ⓒ. $Fe_2O_3$
ⓓ. $MnO_4^-$
Correct Answer: $MnO_4^-$
Explanation: In the permanganate ion ($MnO_4^-$), manganese has a fractional oxidation state due to its involvement in a resonance structure. The oxidation state of manganese can be considered to be an average between +6 and +7 in the different resonance forms of the ion.
103. In the compound $Cr_2O_7^{2-}$ (dichromate ion), what is the fractional oxidation state of chromium?
ⓐ. +3
ⓑ. +6
ⓒ. +2
ⓓ. +5
Correct Answer: +6
Explanation: In the dichromate ion ($Cr_2O_7^{2-}$), the chromium atoms have an average oxidation state of +6. This occurs because the overall oxidation state is averaged over both chromium atoms in the ion, even though the actual oxidation states can vary slightly due to resonance.
104. Why do fractional oxidation states occur in coordination compounds?
ⓐ. Because the central metal atom always has an integer oxidation state
ⓑ. Due to the averaging of oxidation states in resonance structures
ⓒ. Because ligands never affect oxidation states
ⓓ. Because of the presence of free radicals
Correct Answer: Due to the averaging of oxidation states in resonance structures
Explanation: Fractional oxidation states occur in coordination compounds due to the averaging of oxidation states in resonance structures. The metal center may have multiple oxidation states that combine in different resonance forms, resulting in a fractional oxidation state.
105. In the complex ion $[Fe(CO)_5]$, what is the fractional oxidation state of iron?
ⓐ. +2
ⓑ. +1
ⓒ. +3
ⓓ. 0
Correct Answer: 0
Explanation: In $[Fe(CO)_5]$, iron has a fractional oxidation state of 0. Carbon monoxide (CO) is a neutral ligand, and the iron atom doesn’t gain or lose electrons from the ligands, resulting in an oxidation state of 0 for iron in this organometallic complex.
106. What is the oxidation state of nitrogen in the compound $N_2O$ (nitrous oxide)?
ⓐ. +1
ⓑ. +2
ⓒ. +3
ⓓ. -1
Correct Answer: +1
Explanation: In nitrous oxide ($N_2O$), the oxidation state of nitrogen is fractional. Since there are two nitrogen atoms, the oxidation state of nitrogen is averaged between +1 and +2. This leads to a fractional oxidation state of nitrogen in the compound.
107. In the molecule $NO_3^-$ (nitrate), what is the fractional oxidation state of nitrogen?
ⓐ. +3
ⓑ. +5
ⓒ. +6
ⓓ. 0
Correct Answer: +5
Explanation: In nitrate ($NO_3^-$), nitrogen has an oxidation state of +5. This is the average oxidation state of nitrogen, as oxygen atoms in this molecule are involved in resonance structures that contribute to the overall oxidation state being fractional when considering all possible forms.
108. Which of the following is an example of a compound where fractional oxidation states occur due to resonance?
ⓐ. $SO_2$
ⓑ. $H_2O_2$
ⓒ. $NO_3^-$
ⓓ. $NaCl$
Correct Answer: $NO_3^-$
Explanation: In the nitrate ion ($NO_3^-$), the oxidation state of nitrogen is fractional due to the resonance of the three oxygen atoms. The nitrogen’s oxidation state is averaged from +5 to +6, resulting in a fractional oxidation state of +5 in the ion.
109. In the compound $K_3[Cr(CO)_6]$, what is the oxidation state of chromium (Cr)?
ⓐ. +2
ⓑ. +3
ⓒ. +6
ⓓ. 0
Correct Answer: +3
Explanation: In the complex $K_3[Cr(CO)_6]$, chromium (Cr) is in the +3 oxidation state. The CO ligand is neutral, so chromium’s oxidation state is determined by the overall charge of the complex, which is neutral, leading to an oxidation state of +3 for chromium.
110. What happens to the oxidation state of an element when fractional oxidation states are observed in a compound?
ⓐ. The element always gains electrons
ⓑ. The element has a non-integer average oxidation state
ⓒ. The oxidation state is always +1
ⓓ. The oxidation state increases by one
Correct Answer: The element has a non-integer average oxidation state
Explanation: When fractional oxidation states are observed, it means that the oxidation state of the element is an average of multiple possible oxidation states, often due to resonance structures or the involvement of multiple oxidation states in the compound.
111. Which of the following ions is an example of a species with fractional oxidation states?
ⓐ. $Fe^{2+}$
ⓑ. $Cu^{2+}$
ⓒ. $Na^+$
ⓓ. $MnO_4^-$
Correct Answer: $MnO_4^-$
Explanation: The permanganate ion ($MnO_4^-$) has a fractional oxidation state for manganese, which arises from its resonance structures. Manganese can have oxidation states between +6 and +7, giving a fractional average oxidation state in the permanganate ion.
112. What is the oxidation state of copper in the complex $[CuCl_4]^{2-}$?
ⓐ. +1
ⓑ. +2
ⓒ. +3
ⓓ. 0
Correct Answer: +2
Explanation: In the complex ion $[CuCl_4]^{2-}$, copper (Cu) has an oxidation state of +2. Each chloride (Cl) ligand has an oxidation number of -1, and the overall charge of the complex is -2, leading to copper having an oxidation number of +2.
113. In the compound $MnO_2$, what is the oxidation number of manganese?
ⓐ. +3
ⓑ. +2
ⓒ. +4
ⓓ. 0
Correct Answer: +4
Explanation: In $MnO_2$, oxygen has an oxidation number of -2. Since there are two oxygen atoms, the total oxidation number for oxygen is -4. To balance this, manganese must have an oxidation number of +4, indicating that it has lost electrons.
114. Which of the following compounds shows the fractional oxidation state of an element?
ⓐ. $SO_3$
ⓑ. $FeCl_3$
ⓒ. $Cr_2O_7^{2-}$
ⓓ. $NaCl$
Correct Answer: $Cr_2O_7^{2-}$
Explanation: In the dichromate ion ($Cr_2O_7^{2-}$), chromium exhibits a fractional oxidation state due to the resonance structures. The oxidation state of chromium is averaged to +6, even though the individual oxidation states may vary slightly in different resonance forms.
115. In the molecule $CO_2$, what is the oxidation number of carbon?
ⓐ. +0
ⓑ. +2
ⓒ. -3
ⓓ. +4
Correct Answer: +4
Explanation: In carbon dioxide ($CO_2$), oxygen has an oxidation number of -2, and the total oxidation number for two oxygen atoms is -4. To balance the charge of 0 on the molecule, carbon must have an oxidation number of +4. This oxidation state is consistent and does not show fractional oxidation.
116. What is meant by variable oxidation states of an element?
ⓐ. An element only has one oxidation state in all compounds
ⓑ. An element has more than one possible oxidation state in different compounds
ⓒ. An element always has a positive oxidation state
ⓓ. An element’s oxidation state does not change in a compound
Correct Answer: An element has more than one possible oxidation state in different compounds
Explanation: Variable oxidation states refer to an element’s ability to exhibit more than one oxidation state in different compounds. This is often seen in transition metals, where the metal can have multiple oxidation states depending on the compound and bonding environment.
117. Which of the following elements shows variable oxidation states?
ⓐ. Sodium
ⓑ. Magnesium
ⓒ. Iron
ⓓ. Chlorine
Correct Answer: Iron
Explanation: Iron is a transition metal that shows variable oxidation states. It commonly exists in +2 and +3 oxidation states, as seen in compounds like iron(II) sulfate ($FeSO_4$) and iron(III) chloride ($FeCl_3$).
118. What is the oxidation state of manganese in $MnO_4^-$ (permanganate ion)?
ⓐ. +2
ⓑ. +4
ⓒ. +5
ⓓ. +7
Correct Answer: +7
Explanation: Manganese in the permanganate ion ($MnO_4^-$) has an oxidation state of +7. This is a high oxidation state, showing that manganese can exhibit variable oxidation states, ranging from +2 to +7, depending on the compound.
119. Which of the following transition metals can exhibit variable oxidation states?
ⓐ. Sodium
ⓑ. Copper
ⓒ. Calcium
ⓓ. Potassium
Correct Answer: Copper
Explanation: Copper is a transition metal that can exhibit variable oxidation states. It commonly appears in +1 and +2 oxidation states, as seen in copper(I) oxide ($Cu_2O$) and copper(II) sulfate ($CuSO_4$).
120. What is the oxidation state of chromium in $Cr_2O_3$ (chromium(III) oxide)?
ⓐ. +6
ⓑ. +3
ⓒ. +2
ⓓ. +4
Correct Answer: +3
Explanation: In chromium(III) oxide ($Cr_2O_3$), chromium has an oxidation state of +3. Chromium is a transition metal known for having multiple oxidation states, ranging from +2 to +6, depending on the compound.
121. Which element commonly shows oxidation states of +2 and +4?
ⓐ. Copper
ⓑ. Manganese
ⓒ. Iron
ⓓ. Lead
Correct Answer: Lead
Explanation: Lead can show oxidation states of +2 and +4, as seen in lead(II) chloride ($PbCl_2$) and lead(IV) oxide ($PbO_2$). These are examples of variable oxidation states in a main-group metal.
122. In which of the following compounds does the element exhibit a +4 oxidation state?
ⓐ. $FeCl_3$
ⓑ. $PbO_2$
ⓒ. $CuO$
ⓓ. $MnO_2$
Correct Answer: $PbO_2$
Explanation: Lead in lead(IV) oxide ($PbO_2$) has an oxidation state of +4. This is an example of the variable oxidation states of lead, which can also exhibit a +2 oxidation state in compounds like $PbCl_2$.
123. Which transition metal exhibits oxidation states from +2 to +7?
ⓐ. Iron
ⓑ. Manganese
ⓒ. Copper
ⓓ. Chromium
Correct Answer: Manganese
Explanation: Manganese can exhibit a wide range of oxidation states from +2 to +7, as seen in compounds like manganese(II) chloride ($MnCl_2$), manganese(IV) oxide ($MnO_2$), and potassium permanganate ($KMnO_4$).
124. What is the oxidation state of copper in $Cu_2O$ (copper(I) oxide)?
ⓐ. +2
ⓑ. +3
ⓒ. +1
ⓓ. 0
Correct Answer: +1
Explanation: In copper(I) oxide ($Cu_2O$), copper has an oxidation state of +1. Copper is known for its ability to exhibit variable oxidation states, including +1 and +2.
125. What is the oxidation state of iron in $FeCl_2$ (iron(II) chloride)?
ⓐ. +3
ⓑ. +2
ⓒ. +1
ⓓ. 0
Correct Answer: +2
Explanation: In iron(II) chloride ($FeCl_2$), iron has an oxidation state of +2. Iron can show variable oxidation states, and in this case, it is in the +2 state. In iron(III) chloride ($FeCl_3$), iron has an oxidation state of +3.
126. Which element has oxidation states ranging from +1 to +3 in its compounds?
ⓐ. Nitrogen
ⓑ. Zinc
ⓒ. Carbon
ⓓ. Iron
Correct Answer: Iron
Explanation: Iron exhibits variable oxidation states, typically ranging from +2 to +3. In compounds like iron(II) chloride ($FeCl_2$) and iron(III) chloride ($FeCl_3$), iron shows these oxidation states.
127. What is the oxidation state of titanium in $TiO_2$ (titanium dioxide)?
ⓐ. +2
ⓑ. +3
ⓒ. +4
ⓓ. 0
Correct Answer: +4
Explanation: In titanium dioxide ($TiO_2$), titanium has an oxidation state of +4. Titanium is a transition metal that can exhibit oxidation states of +2 and +4 in its compounds.
128. What is the oxidation state of gold in $AuCl_4^-$ (gold(III) chloride)?
ⓐ. +1
ⓑ. +2
ⓒ. +3
ⓓ. +4
Correct Answer: +3
Explanation: In gold(III) chloride ($AuCl_4^-$), gold has an oxidation state of +3. Gold can exhibit oxidation states of +1 and +3, with the +3 state being more common in certain compounds like $AuCl_4^-$.
129. Which of the following elements can exhibit oxidation states ranging from +1 to +5?
ⓐ. Vanadium
ⓑ. Nitrogen
ⓒ. Manganese
ⓓ. Chromium
Correct Answer: Vanadium
Explanation: Vanadium is a transition metal that can exhibit oxidation states ranging from +1 to +5, as seen in compounds like vanadium(II) chloride ($VCl_2$) and vanadium pentoxide ($V_2O_5$).
130. What is the oxidation state of copper in $CuSO_4$ (copper(II) sulfate)?
ⓐ. +1
ⓑ. +2
ⓒ. +3
ⓓ. +4
Correct Answer: +2
Explanation: In copper(II) sulfate ($CuSO_4$), copper has an oxidation state of +2. Copper commonly exhibits oxidation states of +1 and +2, with the +2 state being more prevalent in compounds like $CuSO_4$.
131. Which of the following elements shows oxidation states from +1 to +6?
ⓐ. Chromium
ⓑ. Manganese
ⓒ. Iron
ⓓ. Lead
Correct Answer: Chromium
Explanation: Chromium can exhibit oxidation states from +1 to +6. For example, in chromium(I) chloride ($CrCl$), chromium has an oxidation state of +1, while in chromium(VI) oxide ($CrO_3$), chromium has an oxidation state of +6.
132. How is the oxidation number useful in balancing redox reactions?
ⓐ. It helps identify the number of protons in a molecule
ⓑ. It determines the total charge of the compound
ⓒ. It helps identify the number of electrons gained or lost
ⓓ. It indicates the molecular weight of the compound
Correct Answer: It helps identify the number of electrons gained or lost
Explanation: The oxidation number helps determine the number of electrons lost in oxidation and the number of electrons gained in reduction, which is crucial for balancing redox reactions. The change in oxidation states of the elements involved can be used to balance the electrons in the reaction.
133. Which method uses oxidation numbers to balance redox reactions?
ⓐ. Half-reaction method
ⓑ. Oxidation number method
ⓒ. Direct balance method
ⓓ. Atomic method
Correct Answer: Oxidation number method
Explanation: The oxidation number method is used to balance redox reactions by tracking the changes in oxidation states of the elements. This method involves adjusting coefficients to ensure that the total increase in oxidation number (electron loss) equals the total decrease in oxidation number (electron gain).
134. In the reaction $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$, how do the oxidation numbers help balance the reaction?
ⓐ. They identify the number of protons involved
ⓑ. They determine the number of electrons exchanged between zinc and copper
ⓒ. They determine the atomic masses of zinc and copper
ⓓ. They identify the molecular weight of the compounds
Correct Answer: They determine the number of electrons exchanged between zinc and copper
Explanation: In this reaction, zinc is oxidized from an oxidation number of 0 to +2, losing two electrons. Copper is reduced from +2 to 0, gaining those two electrons. The oxidation number changes help identify the number of electrons exchanged, which is crucial for balancing the reaction.
135. In the reaction $2MnO_4^- + 16H^+ + 10e^- \rightarrow 2Mn^{2+} + 8H_2O$, how do the oxidation numbers of manganese change?
ⓐ. Manganese is reduced from +7 to +4
ⓑ. Manganese is oxidized from +4 to +7
ⓒ. Manganese is reduced from +7 to +2
ⓓ. Manganese remains at +4
Correct Answer: Manganese is reduced from +7 to +2
Explanation: In this reaction, manganese in the permanganate ion ($MnO_4^-$) has an oxidation number of +7. In the product, manganese in the $Mn^{2+}$ ion has an oxidation number of +2. Therefore, manganese is reduced from +7 to +2.
136. In balancing redox reactions using the oxidation number method, what must be equal on both sides of the equation?
ⓐ. The number of atoms
ⓑ. The total energy
ⓒ. The total charge
ⓓ. The number of electrons in the reaction
Correct Answer: The total charge
Explanation: When balancing redox reactions using the oxidation number method, the total charge on both sides of the equation must be equal. This ensures that the overall charge is conserved in the reaction.
137. In the reaction $3Fe^{3+} + 3e^- \rightarrow Fe^{0}$, how is the oxidation state of iron (Fe) changing?
ⓐ. Fe is reduced from +3 to +2
ⓑ. Fe is reduced from +2 to 0
ⓒ. Fe is oxidized from 0 to +3
ⓓ. Fe is reduced from +3 to 0
Correct Answer: Fe is reduced from +3 to 0
Explanation: In this reaction, iron is reduced from an oxidation state of +3 in $Fe^{3+}$ to 0 in elemental iron ($Fe$). The gain of electrons (3 electrons) results in a reduction of the oxidation number of iron.
138. In the reaction $Cl_2 + 2e^- \rightarrow 2Cl^-$, what is the change in the oxidation state of chlorine?
ⓐ. Chlorine is oxidized from 0 to -1
ⓑ. Chlorine is reduced from +1 to 0
ⓒ. Chlorine is reduced from 0 to -1
ⓓ. Chlorine is oxidized from -1 to 0
Correct Answer: Chlorine is reduced from 0 to -1
Explanation: In this reaction, chlorine ($Cl_2$) has an oxidation number of 0 and gains electrons to form chloride ions ($Cl^-$), where the oxidation state of chlorine is -1. This is a reduction process.
139. Which of the following is true when balancing redox reactions using oxidation numbers?
ⓐ. The total number of atoms must be balanced but not the charge
ⓑ. The total charge on both sides must be balanced
ⓒ. The number of electrons is not important
ⓓ. Oxidation states are not used in balancing the reaction
Correct Answer: The total charge on both sides must be balanced
Explanation: When using oxidation numbers to balance redox reactions, both the total number of atoms and the total charge on both sides of the reaction must be balanced. This ensures the reaction is both atomically and electrically balanced.
140. In the redox reaction $Zn + 2H^+ \rightarrow Zn^{2+} + H_2$, how do the oxidation states of zinc and hydrogen change?
ⓐ. Zinc is reduced and hydrogen is oxidized
ⓑ. Zinc is oxidized and hydrogen is reduced
ⓒ. Zinc and hydrogen both undergo oxidation
ⓓ. Neither zinc nor hydrogen undergoes oxidation or reduction
Correct Answer: Zinc is oxidized and hydrogen is reduced
Explanation: In this reaction, zinc ($Zn$) is oxidized from an oxidation state of 0 to +2, while hydrogen ions ($H^+$) are reduced from +1 to 0 as they form hydrogen gas ($H_2$). Therefore, zinc is oxidized and hydrogen is reduced.
141. In the reaction $Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O$, how do the oxidation numbers of chromium change?
ⓐ. Chromium is reduced from +3 to +6
ⓑ. Chromium is reduced from +6 to +2
ⓒ. Chromium is reduced from +6 to +3
ⓓ. Chromium is oxidized from +3 to +6
Correct Answer: Chromium is reduced from +6 to +3
Explanation: In this reaction, chromium in the dichromate ion ($Cr_2O_7^{2-}$) has an oxidation state of +6. In the product, chromium in the $Cr^{3+}$ ion has an oxidation state of +3. Therefore, chromium is reduced from +6 to +3 by gaining electrons.
142. In a redox reaction, how can the oxidation numbers help determine the number of electrons exchanged?
ⓐ. By looking at the changes in the oxidation states of the elements
ⓑ. By balancing the atoms on both sides of the equation
ⓒ. By using the mass balance method
ⓓ. By checking the charge balance only
Correct Answer: By looking at the changes in the oxidation states of the elements
Explanation: The number of electrons exchanged in a redox reaction can be determined by calculating the changes in oxidation numbers of the elements involved. The total increase in oxidation numbers (electron loss) must equal the total decrease in oxidation numbers (electron gain).
143. In the reaction $2MnO_4^- + 3e^- + 4H^+ \rightarrow 2Mn^{2+} + 2H_2O$, what happens to manganese?
ⓐ. Manganese is oxidized from +2 to +7
ⓑ. Manganese is reduced from +7 to +2
ⓒ. Manganese is reduced from +4 to +2
ⓓ. Manganese is oxidized from +2 to +4
Correct Answer: Manganese is reduced from +7 to +2
Explanation: In this reaction, manganese in the permanganate ion ($MnO_4^-$) has an oxidation state of +7. In the product, manganese in the $Mn^{2+}$ ion has an oxidation state of +2. Therefore, manganese is reduced from +7 to +2 by gaining electrons.
144. What does balancing a redox reaction using oxidation numbers require?
ⓐ. Equating the number of atoms of each element
ⓑ. Ensuring the total increase in oxidation number equals the total decrease
ⓒ. Ignoring the charge balance
ⓓ. Focusing only on the number of electrons involved
Correct Answer: Ensuring the total increase in oxidation number equals the total decrease
Explanation: When balancing a redox reaction using oxidation numbers, the total increase in oxidation number (electron loss) must equal the total decrease in oxidation number (electron gain). This ensures the electrons are properly accounted for in the reaction.
145. What is a combination reaction?
ⓐ. A reaction where two or more substances combine to form a single product
ⓑ. A reaction where one substance decomposes into two or more products
ⓒ. A reaction where elements exchange ions
ⓓ. A reaction where a compound is broken into its elements
Correct Answer: A reaction where two or more substances combine to form a single product
Explanation: A combination reaction is a type of chemical reaction in which two or more reactants combine to form a single product. These reactions are also known as synthesis reactions.
146. Which of the following is an example of a combination reaction?
ⓐ. $Na + Cl_2 \rightarrow NaCl$
ⓑ. $2NaCl \rightarrow 2Na + Cl_2$
ⓒ. $CaCO_3 \rightarrow CaO + CO_2$
ⓓ. $H_2 + O_2 \rightarrow H_2O$
Correct Answer: $H_2 + O_2 \rightarrow H_2O$
Explanation: In this reaction, hydrogen gas ($H_2$) and oxygen gas ($O_2$) combine to form water ($H_2O$), making it a classic example of a combination reaction, where two reactants form a single product.
147. In a combination reaction, how many products are formed?
ⓐ. One product
ⓑ. Two products
ⓒ. Multiple products
ⓓ. No products are formed
Correct Answer: One product
Explanation: In a combination reaction, two or more reactants combine to form a single product. This is the key characteristic of combination reactions, as opposed to decomposition or displacement reactions.
148. Which of the following reactions is a combination reaction?
ⓐ. $C + O_2 \rightarrow CO_2$
ⓑ. $2NaCl \rightarrow 2Na + Cl_2$
ⓒ. $NaOH + HCl \rightarrow NaCl + H_2O$
ⓓ. $CuSO_4 \rightarrow CuO + SO_3$
Correct Answer: $C + O_2 \rightarrow CO_2$
Explanation: In this reaction, carbon ($C$) and oxygen ($O_2$) combine to form carbon dioxide ($CO_2$), which is a combination reaction. The reactants combine to form a single product.
149. What is the general form of a combination reaction?
ⓐ. $AB \rightarrow A + B$
ⓑ. $A + B \rightarrow AB$
ⓒ. $A + B \rightarrow C + D$
ⓓ. $A \rightarrow B + C$
Correct Answer: $A + B \rightarrow AB$
Explanation: The general form of a combination reaction is when two or more reactants combine to form a single product, represented as $A + B \rightarrow AB$. This highlights the merging of reactants to form a compound.
150. Which of the following is an example of a combination reaction involving elements and compounds?
ⓐ. $2Na + Cl_2 \rightarrow 2NaCl$
ⓑ. $NaCl \rightarrow Na + Cl_2$
ⓒ. $C + O_2 \rightarrow CO_2$
ⓓ. $CaO + CO_2 \rightarrow CaCO_3$
Correct Answer: $2Na + Cl_2 \rightarrow 2NaCl$
Explanation: This is a combination reaction where the elements sodium ($Na$) and chlorine ($Cl_2$) combine to form the compound sodium chloride ($NaCl$).
151. Which of the following reactions is a combination reaction involving two compounds?
ⓐ. $NaOH + HCl \rightarrow NaCl + H_2O$
ⓑ. $C + O_2 \rightarrow CO_2$
ⓒ. $CaO + CO_2 \rightarrow CaCO_3$
ⓓ. $2H_2 + O_2 \rightarrow 2H_2O$
Correct Answer: $CaO + CO_2 \rightarrow CaCO_3$
Explanation: In this reaction, calcium oxide ($CaO$) and carbon dioxide ($CO_2$) combine to form calcium carbonate ($CaCO_3$), which is an example of a combination reaction involving two compounds.
152. Which of the following is true about combination reactions?
ⓐ. Only gases can participate in combination reactions
ⓑ. Combination reactions always involve a metal
ⓒ. Combination reactions involve the combination of two or more substances to form a single product
ⓓ. Combination reactions result in multiple products
Correct Answer: Combination reactions involve the combination of two or more substances to form a single product
Explanation: Combination reactions always involve the merging of two or more substances (either elements or compounds) to form a single product. These reactions can involve solids, liquids, or gases.
153. In the reaction $N_2 + 3H_2 \rightarrow 2NH_3$, what type of reaction is this?
ⓐ. Decomposition
ⓑ. Combination
ⓒ. Displacement
ⓓ. Double displacement
Correct Answer: Combination
Explanation: In this reaction, nitrogen ($N_2$) and hydrogen ($H_2$) combine to form ammonia ($NH_3$), which is a combination reaction. Two reactants combine to form a single product.
154. What is formed in the combination reaction between hydrogen and oxygen?
ⓐ. Hydrogen peroxide
ⓑ. Oxygen gas
ⓒ. Hydrogen chloride
ⓓ. Water
Correct Answer: Water
Explanation: When hydrogen ($H_2$) and oxygen ($O_2$) combine, they form water ($H_2O$), which is a typical combination reaction where two reactants combine to form a single product.
155. Which of the following combinations results in a combination reaction?
ⓐ. $Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl$
ⓑ. $C + O_2 \rightarrow CO_2$
ⓒ. $CaCO_3 \rightarrow CaO + CO_2$
ⓓ. $2H_2O \rightarrow 2H_2 + O_2$
Correct Answer: $C + O_2 \rightarrow CO_2$
Explanation: In this reaction, carbon ($C$) and oxygen ($O_2$) combine to form carbon dioxide ($CO_2$), which is a combination reaction. Two reactants combine to form a single product.
156. Which of the following reactions is NOT a combination reaction?
ⓐ. $N_2 + 3H_2 \rightarrow 2NH_3$
ⓑ. $C + O_2 \rightarrow CO_2$
ⓒ. $H_2O \rightarrow H_2 + O_2$
ⓓ. $Na + Cl_2 \rightarrow NaCl$
Correct Answer: $H_2O \rightarrow H_2 + O_2$
Explanation: This reaction is a decomposition reaction, not a combination reaction. In this case, water ($H_2O$) decomposes into hydrogen ($H_2$) and oxygen ($O_2$), which is the opposite of a combination reaction.
157. In the reaction $P_4 + 5O_2 \rightarrow 2P_2O_5$, what type of reaction is this?
ⓐ. Decomposition
ⓑ. Redox
ⓒ. Displacement
ⓓ. Combination
Correct Answer: Combination
Explanation: In this reaction, phosphorus ($P_4$) and oxygen ($O_2$) combine to form phosphorus pentoxide ($P_2O_5$), making it a combination reaction where two substances combine to form a single product.
158. What is formed when calcium (Ca) reacts with oxygen (O)?
ⓐ. Calcium oxide ($CaO$)
ⓑ. Calcium hydroxide ($Ca(OH)_2$)
ⓒ. Calcium carbonate ($CaCO_3$)
ⓓ. Calcium chloride ($CaCl_2$)
Correct Answer: Calcium oxide ($CaO$)
Explanation: When calcium ($Ca$) reacts with oxygen ($O_2$), calcium oxide ($CaO$) is formed. This is an example of a combination reaction where two elements combine to form a compound.
159. Which of the following reactions is an example of a combination reaction between a metal and a non-metal?
ⓐ. $Na + Cl_2 \rightarrow NaCl$
ⓑ. $H_2O \rightarrow H_2 + O_2$
ⓒ. $C + O_2 \rightarrow CO_2$
ⓓ. $CaCO_3 \rightarrow CaO + CO_2$
Correct Answer: $Na + Cl_2 \rightarrow NaCl$
Explanation: In this reaction, sodium (a metal) reacts with chlorine (a non-metal) to form sodium chloride ($NaCl$), a classic example of a combination reaction between a metal and a non-metal.
160. What is a decomposition reaction?
ⓐ. A reaction where two or more substances combine to form a single product
ⓑ. A reaction where a single compound breaks down into two or more simpler substances
ⓒ. A reaction where elements exchange places
ⓓ. A reaction where a substance gains electrons
Correct Answer: A reaction where a single compound breaks down into two or more simpler substances
Explanation: A decomposition reaction occurs when a single compound breaks down into two or more simpler substances, often due to heating, light, or electrical energy. This is the opposite of a combination reaction.
161. Which of the following is an example of a decomposition reaction?
ⓐ. $2Na + Cl_2 \rightarrow 2NaCl$
ⓑ. $CaCO_3 \rightarrow CaO + CO_2$
ⓒ. $H_2 + O_2 \rightarrow H_2O$
ⓓ. $NaOH + HCl \rightarrow NaCl + H_2O$
Correct Answer: $CaCO_3 \rightarrow CaO + CO_2$
Explanation: This is a decomposition reaction where calcium carbonate ($CaCO_3$) breaks down into calcium oxide ($CaO$) and carbon dioxide ($CO_2$) upon heating. This type of reaction is common for salts that decompose under heat.
162. Which of the following is the correct general form of a decomposition reaction?
ⓐ. $A + B \rightarrow AB$
ⓑ. $AB \rightarrow A + B$
ⓒ. $A + B + C \rightarrow ABC$
ⓓ. $AB + C \rightarrow AC + B$
Correct Answer: $AB \rightarrow A + B$
Explanation: A decomposition reaction has the general form $AB \rightarrow A + B$, where a single compound ($AB$) breaks down into two or more simpler substances ($A$ and $B$).
163. In the decomposition of hydrogen peroxide ($H_2O_2$), what are the products?
ⓐ. Water and oxygen
ⓑ. Water and hydrogen
ⓒ. Oxygen and hydrogen
ⓓ. Oxygen and carbon dioxide
Correct Answer: Water and oxygen
Explanation: The decomposition of hydrogen peroxide ($H_2O_2$) produces water ($H_2O$) and oxygen gas ($O_2$). The reaction is typically catalyzed by light or the enzyme catalase: $2H_2O_2 \rightarrow 2H_2O + O_2$.
164. What type of energy is typically required for a decomposition reaction to occur?
ⓐ. Thermal energy (heat)
ⓑ. Electrical energy
ⓒ. Light energy
ⓓ. All of the above
Correct Answer: All of the above
Explanation: Decomposition reactions often require energy input in the form of heat (thermal energy), light energy, or electrical energy. For example, heating calcium carbonate causes it to decompose into calcium oxide and carbon dioxide.
165. Which of the following reactions is an example of a thermal decomposition reaction?
ⓐ. $2NaCl \rightarrow 2Na + Cl_2$
ⓑ. $CaCO_3 \rightarrow CaO + CO_2$
ⓒ. $H_2 + Cl_2 \rightarrow 2HCl$
ⓓ. $NaOH + HCl \rightarrow NaCl + H_2O$
Correct Answer: $CaCO_3 \rightarrow CaO + CO_2$
Explanation: The decomposition of calcium carbonate ($CaCO_3$) into calcium oxide ($CaO$) and carbon dioxide ($CO_2$) is an example of thermal decomposition, as heat is required to break down the compound.
166. In the reaction $2NaCl \rightarrow 2Na + Cl_2$, what type of reaction is this?
ⓐ. Decomposition reaction
ⓑ. Combination reaction
ⓒ. Displacement reaction
ⓓ. Redox reaction
Correct Answer: Decomposition reaction
Explanation: In this reaction, sodium chloride ($NaCl$) decomposes into sodium metal ($Na$) and chlorine gas ($Cl_2$). This is an example of a decomposition reaction where a single substance breaks down into two simpler substances.
167. Which of the following reactions is an example of electrolysis, a type of decomposition reaction?
ⓐ. $2H_2O \rightarrow 2H_2 + O_2$
ⓑ. $CaCO_3 \rightarrow CaO + CO_2$
ⓒ. $2NaCl \rightarrow 2Na + Cl_2$
ⓓ. $H_2 + O_2 \rightarrow H_2O$
Correct Answer: $2H_2O \rightarrow 2H_2 + O_2$
Explanation: The decomposition of water into hydrogen and oxygen gases using electrical energy is an example of electrolysis, a type of decomposition reaction. It involves the breakdown of a compound using an electric current.
168. In the decomposition reaction $2KClO_3 \rightarrow 2KCl + 3O_2$, what type of reaction is this?
ⓐ. Redox reaction
ⓑ. Combustion
ⓒ. Thermal decomposition
ⓓ. Electrolysis
Correct Answer: Thermal decomposition
Explanation: The decomposition of potassium chlorate ($KClO_3$) into potassium chloride ($KCl$) and oxygen gas ($O_2$) is an example of thermal decomposition, as heat is required to break down the compound.
169. Which of the following compounds undergoes thermal decomposition?
ⓐ. $CaCO_3$
ⓑ. $NaCl$
ⓒ. $H_2O$
ⓓ. $NaOH$
Correct Answer: $CaCO_3$
Explanation: Calcium carbonate ($CaCO_3$) undergoes thermal decomposition when heated to form calcium oxide ($CaO$) and carbon dioxide ($CO_2$). This is a common example of a thermal decomposition reaction.
170. What are the products of the decomposition of potassium nitrate ($KNO_3$) when heated?
ⓐ. Potassium hydroxide and oxygen
ⓑ. Potassium and nitrogen
ⓒ. Potassium and oxygen
ⓓ. Potassium nitrite and oxygen
Correct Answer: Potassium nitrite and oxygen
Explanation: When potassium nitrate ($KNO_3$) is heated, it decomposes into potassium nitrite ($KNO_2$) and oxygen gas ($O_2$). The reaction is: $2KNO_3 \rightarrow 2KNO_2 + O_2$.
171. In the reaction $2HgO \rightarrow 2Hg + O_2$, what type of reaction is this?
ⓐ. Decomposition reaction
ⓑ. Combustion reaction
ⓒ. Neutralization reaction
ⓓ. Synthesis reaction
Correct Answer: Decomposition reaction
Explanation: This is a decomposition reaction where mercuric oxide ($HgO$) decomposes into mercury ($Hg$) and oxygen ($O_2$) upon heating. The compound breaks down into two simpler substances.
172. Which of the following is an example of a photochemical decomposition reaction?
ⓐ. $2NaCl \rightarrow 2Na + Cl_2$
ⓑ. $2H_2O \rightarrow 2H_2 + O_2$ (in the presence of sunlight)
ⓒ. $CaCO_3 \rightarrow CaO + CO_2$
ⓓ. $NaCl + H_2O \rightarrow NaOH + HCl$
Correct Answer: $2H_2O \rightarrow 2H_2 + O_2$ (in the presence of sunlight)
Explanation: Photochemical decomposition occurs when light energy is used to decompose a compound. In this case, the decomposition of water ($H_2O$) into hydrogen and oxygen occurs in the presence of sunlight, making it a photochemical reaction.
173. Which of the following statements is true about decomposition reactions?
ⓐ. Decomposition reactions always require light energy
ⓑ. Decomposition reactions always involve oxygen
ⓒ. Decomposition reactions break down a single reactant into simpler products
ⓓ. Decomposition reactions always produce only one product
Correct Answer: Decomposition reactions break down a single reactant into simpler products
Explanation: Decomposition reactions involve the breakdown of a single reactant into two or more simpler products. These reactions may require heat, light, or electricity but do not always involve oxygen, and they can produce more than one product.
174. In the decomposition of hydrogen peroxide, what type of reaction is occurring?
ⓐ. Neutralization
ⓑ. Combustion
ⓒ. Synthesis
ⓓ. Decomposition
Correct Answer: Decomposition
Explanation: The decomposition of hydrogen peroxide ($H_2O_2$) is a classic example of a decomposition reaction. It breaks down into water ($H_2O$) and oxygen gas ($O_2$): $2H_2O_2 \rightarrow 2H_2O + O_2$.
175. What is the product of the decomposition of calcium hydroxide ($Ca(OH)_2$) under heat?
ⓐ. Calcium oxide and water
ⓑ. Calcium carbonate and water
ⓒ. Calcium and oxygen
ⓓ. Calcium oxide and carbon dioxide
Correct Answer: Calcium oxide and water
Explanation: When calcium hydroxide ($Ca(OH)_2$) is heated, it decomposes into calcium oxide ($CaO$) and water ($H_2O$). This is an example of a thermal decomposition reaction.
176. What is a displacement reaction?
ⓐ. A reaction where two substances exchange their ions
ⓑ. A reaction where one element displaces another element from a compound
ⓒ. A reaction where a substance breaks down into simpler products
ⓓ. A reaction where no ions are involved
Correct Answer: A reaction where one element displaces another element from a compound
Explanation: A displacement reaction occurs when one element displaces another from a compound. This can occur with metals (metal displacement) or non-metals (non-metal displacement), depending on the reactivity of the elements involved.
177. Which of the following is an example of a metal displacement reaction?
ⓐ. $CuSO_4 + Zn \rightarrow ZnSO_4 + Cu$
ⓑ. $NaCl + AgNO_3 \rightarrow NaNO_3 + AgCl$
ⓒ. $H_2 + Cl_2 \rightarrow 2HCl$
ⓓ. $Mg + H_2O \rightarrow Mg(OH)_2 + H_2$
Correct Answer: $CuSO_4 + Zn \rightarrow ZnSO_4 + Cu$
Explanation: In this reaction, zinc ($Zn$), a more reactive metal, displaces copper ($Cu$) from copper(II) sulfate ($CuSO_4$), forming zinc sulfate ($ZnSO_4$) and copper metal ($Cu$). This is a classic example of a metal displacement reaction.
178. Which metal can displace copper from a solution of copper sulfate ($CuSO_4$)?
ⓐ. Iron
ⓑ. Lead
ⓒ. Zinc
ⓓ. Silver
Correct Answer: Zinc
Explanation: Zinc is more reactive than copper and can displace copper from copper sulfate. The reaction would be $Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$. Less reactive metals like lead or silver cannot displace copper from copper sulfate.
179. What happens in a non-metal displacement reaction?
ⓐ. One metal displaces another metal
ⓑ. One non-metal displaces another non-metal from a compound
ⓒ. A non-metal displaces a metal from a compound
ⓓ. A metal displaces a non-metal from a compound
Correct Answer: One non-metal displaces another non-metal from a compound
Explanation: In a non-metal displacement reaction, a more reactive non-metal displaces a less reactive non-metal from a compound. For example, chlorine ($Cl_2$) can displace bromine from sodium bromide ($NaBr$).
180. Which of the following is an example of a non-metal displacement reaction?
ⓐ. $Fe + CuSO_4 \rightarrow FeSO_4 + Cu$
ⓑ. $H_2 + Cl_2 \rightarrow 2HCl$
ⓒ. $Na + Cl_2 \rightarrow NaCl$
ⓓ. $Mg + H_2O \rightarrow Mg(OH)_2 + H_2$
Correct Answer: $H_2 + Cl_2 \rightarrow 2HCl$
Explanation: In this reaction, hydrogen gas ($H_2$) displaces chlorine from chlorine gas ($Cl_2$), forming hydrogen chloride ($HCl$). This is an example of a non-metal displacement reaction, where one non-metal (hydrogen) replaces another (chlorine) in a compound.
181. What is the result of the reaction between zinc and hydrochloric acid ($Zn + 2HCl \rightarrow ZnCl_2 + H_2$)?
ⓐ. Zinc displaces hydrogen from hydrochloric acid
ⓑ. Zinc displaces chlorine from hydrochloric acid
ⓒ. Hydrogen displaces zinc from hydrochloric acid
ⓓ. Hydrogen displaces chlorine from hydrochloric acid
Correct Answer: Zinc displaces hydrogen from hydrochloric acid
Explanation: In this reaction, zinc ($Zn$) displaces hydrogen ($H$) from hydrochloric acid ($HCl$) to form zinc chloride ($ZnCl_2$) and hydrogen gas ($H_2$). This is a typical example of a metal displacement reaction.
182. Which of the following is a possible product of the reaction between magnesium and copper sulfate ($CuSO_4$)?
ⓐ. Magnesium sulfate and copper
ⓑ. Magnesium sulfate and iron
ⓒ. Copper sulfate and magnesium
ⓓ. Iron sulfate and magnesium
Correct Answer: Magnesium sulfate and copper
Explanation: In this metal displacement reaction, magnesium ($Mg$) is more reactive than copper ($Cu$) and will displace copper from copper sulfate ($CuSO_4$), producing magnesium sulfate ($MgSO_4$) and copper metal ($Cu$): $Mg + CuSO_4 \rightarrow MgSO_4 + Cu$.
183. In the reaction $Cl_2 + 2NaBr \rightarrow 2NaCl + Br_2$, what type of reaction is this?
ⓐ. Metal displacement reaction
ⓑ. Redox reaction
ⓒ. Synthesis reaction
ⓓ. Non-metal displacement reaction
Correct Answer: Non-metal displacement reaction
Explanation: This is a non-metal displacement reaction where chlorine ($Cl_2$) displaces bromine ($Br$) from sodium bromide ($NaBr$) to form sodium chloride ($NaCl$) and bromine gas ($Br_2$).
184. Which of the following statements is true about displacement reactions?
ⓐ. Only metals can be involved in displacement reactions
ⓑ. A more reactive element can displace a less reactive element from a compound
ⓒ. A less reactive element can displace a more reactive element
ⓓ. Displacement reactions always result in the formation of a precipitate
Correct Answer: A more reactive element can displace a less reactive element from a compound
Explanation: In displacement reactions, a more reactive element can displace a less reactive element from a compound. For example, a more reactive metal can displace a less reactive metal from its compound, and a more reactive non-metal can displace a less reactive non-metal.
185. Which of the following is the product of the reaction between chlorine gas and potassium bromide ($Cl_2 + 2KBr \rightarrow 2KCl + Br_2$)?
ⓐ. Potassium chloride and hydrogen gas
ⓑ. Potassium bromide and chlorine gas
ⓒ. Potassium chloride and bromine gas
ⓓ. Potassium chloride and oxygen gas
Correct Answer: Potassium chloride and bromine gas
Explanation: In this non-metal displacement reaction, chlorine ($Cl_2$) displaces bromine ($Br$) from potassium bromide ($KBr$), producing potassium chloride ($KCl$) and bromine gas ($Br_2$).
186. In a metal displacement reaction, what determines whether one metal can displace another from a compound?
ⓐ. The atomic weight of the metals
ⓑ. The reactivity of the metals
ⓒ. The color of the metals
ⓓ. The temperature of the reaction
Correct Answer: The reactivity of the metals
Explanation: In metal displacement reactions, a more reactive metal can displace a less reactive metal from its compound. The reactivity of the metals determines which metal can replace the other. More reactive metals (such as zinc) can displace less reactive metals (such as copper).
187. Which of the following is NOT an example of a displacement reaction?
ⓐ. $Fe + CuSO_4 \rightarrow FeSO_4 + Cu$
ⓑ. $Na + H_2O \rightarrow NaOH + H_2$
ⓒ. $CaCO_3 \rightarrow CaO + CO_2$
ⓓ. $Cl_2 + 2NaBr \rightarrow 2NaCl + Br_2$
Correct Answer: $CaCO_3 \rightarrow CaO + CO_2$
Explanation: This is a decomposition reaction, not a displacement reaction. In a displacement reaction, an element displaces another element from a compound, but in this case, calcium carbonate ($CaCO_3$) breaks down into calcium oxide ($CaO$) and carbon dioxide ($CO_2$) without the involvement of another element displacing a compound.
188. What happens in a non-metal displacement reaction?
ⓐ. A metal displaces a non-metal
ⓑ. A non-metal displaces a metal
ⓒ. A non-metal displaces another non-metal
ⓓ. A metal displaces another metal
Correct Answer: A non-metal displaces another non-metal
Explanation: In a non-metal displacement reaction, a more reactive non-metal displaces a less reactive non-metal from its compound. For example, chlorine can displace bromine from sodium bromide.
189. What is the driving force behind displacement reactions?
ⓐ. The formation of a precipitate
ⓑ. The increase in temperature
ⓒ. The movement of electrons
ⓓ. The displacement of a more reactive element
Correct Answer: The displacement of a more reactive element
Explanation: In displacement reactions, a more reactive element displaces a less reactive element from a compound. This is the driving force behind these reactions, as the more reactive element takes the place of the less reactive one.
190. What is a disproportionation reaction?
ⓐ. A reaction in which a single element undergoes both oxidation and reduction
ⓑ. A reaction in which two elements exchange places
ⓒ. A reaction in which a compound is synthesized from simpler substances
ⓓ. A reaction in which a substance breaks down into its components
Correct Answer: A reaction in which a single element undergoes both oxidation and reduction
Explanation: A disproportionation reaction is a type of redox reaction in which a single substance is both oxidized and reduced, resulting in two different products. The element undergoes oxidation (loses electrons) and reduction (gains electrons) simultaneously.
191. Which of the following is an example of a disproportionation reaction?
ⓐ. $2Na + Cl_2 \rightarrow 2NaCl$
ⓑ. $3H_2O_2 \rightarrow 2H_2O + O_2$
ⓒ. $2H_2 + O_2 \rightarrow 2H_2O$
ⓓ. $C + O_2 \rightarrow CO_2$
Correct Answer: $3H_2O_2 \rightarrow 2H_2O + O_2$
Explanation: In this reaction, hydrogen peroxide ($H_2O_2$) undergoes disproportionation. Some molecules are reduced to water ($H_2O$), while others are oxidized to oxygen gas ($O_2$). This is a classic example of disproportionation.
192. In the reaction $3H_2O_2 \rightarrow 2H_2O + O_2$, what happens to oxygen in hydrogen peroxide?
ⓐ. Oxygen is reduced
ⓑ. Oxygen is oxidized
ⓒ. Oxygen remains unchanged
ⓓ. Oxygen is displaced
Correct Answer: Oxygen is oxidized
Explanation: In this reaction, hydrogen peroxide ($H_2O_2$) undergoes disproportionation. The oxygen in $H_2O_2$ is both reduced to form water ($H_2O$) and oxidized to form oxygen gas ($O_2$). The oxidation state of oxygen increases in the formation of $O_2$, meaning oxygen is oxidized.
193. Which of the following substances undergoes disproportionation in acidic solution?
ⓐ. Sodium
ⓑ. Potassium
ⓒ. Hydrogen
ⓓ. Chlorine
Correct Answer: Chlorine
Explanation: Chlorine ($Cl_2$) can undergo disproportionation in acidic solution to form both chloride ($Cl^-$) and chlorine ($Cl_2$) gas. The reaction is: $Cl_2 + 2H^+ \rightarrow Cl^- + Cl_2$.
194. In the reaction $2Cu^+ \rightarrow Cu + Cu^{2+}$, what happens to copper?
ⓐ. Copper is reduced
ⓑ. Copper is oxidized
ⓒ. Copper undergoes no change
ⓓ. Copper is displaced by another metal
Correct Answer: Copper is oxidized
Explanation: In this reaction, copper in the +1 oxidation state ($Cu^+$) is oxidized to copper in the +2 oxidation state ($Cu^{2+}$), while some copper is reduced to elemental copper ($Cu$). This is an example of a disproportionation reaction where copper undergoes both oxidation and reduction.
195. What is the oxidation state of chlorine in $Cl_2$ before and after disproportionation in the reaction $Cl_2 + 2H_2O \rightarrow HCl + HOCl$?
ⓐ. +1 before, -1 after
ⓑ. -1 before, +1 after
ⓒ. +1 before, +1 after
ⓓ. 0 before, +1 and -1 after
Correct Answer: 0 before, +1 and -1 after
Explanation: In this disproportionation reaction, chlorine ($Cl_2$) undergoes both oxidation and reduction. Before the reaction, chlorine has an oxidation state of 0. After the reaction, one chlorine atom is reduced to -1 in $HCl$, and the other is oxidized to +1 in $HOCl$.
196. Which of the following is an example of a disproportionation reaction involving sulfur?
ⓐ. $SO_2 + H_2O \rightarrow H_2SO_3$
ⓑ. $2NaCl \rightarrow 2Na + Cl_2$
ⓒ. $2Na + Cl_2 \rightarrow 2NaCl$
ⓓ. $3SO_2 \rightarrow 2SO_3 + SO_2$
Correct Answer: $SO_2 + H_2O \rightarrow H_2SO_3$
Explanation: In this reaction, sulfur dioxide ($SO_2$) undergoes disproportionation in the presence of water. The sulfur atom in $SO_2$ is simultaneously oxidized to sulfur trioxide ($SO_3$) and reduced to sulfur dioxide ($SO_2$).
197. Which of the following elements is commonly involved in disproportionation reactions?
ⓐ. Sodium
ⓑ. Chlorine
ⓒ. Potassium
ⓓ. Lithium
Correct Answer: Chlorine
Explanation: Chlorine is a common element involved in disproportionation reactions, where it can be simultaneously oxidized and reduced. A common example is the reaction $Cl_2 + 2H_2O \rightarrow HCl + HOCl$, where chlorine is both reduced and oxidized.
198. Which compound undergoes disproportionation to form oxygen gas and water in a reaction?
ⓐ. $NaCl$
ⓑ. $NaOH$
ⓒ. $O_2$
ⓓ. $H_2O_2$
Correct Answer: $H_2O_2$
Explanation: Hydrogen peroxide ($H_2O_2$) undergoes disproportionation to form water ($H_2O$) and oxygen gas ($O_2$) in the reaction: $3H_2O_2 \rightarrow 2H_2O + O_2$. This is a classic disproportionation reaction where one substance is both oxidized and reduced.
199. In the reaction $2Cu^+ \rightarrow Cu + Cu^{2+}$, what type of reaction is this?
ⓐ. Decomposition
ⓑ. Combination
ⓒ. Disproportionation
ⓓ. Redox reaction without disproportionation
Correct Answer: Disproportionation
Explanation: In this reaction, copper($Cu^+$) undergoes disproportionation, where it is simultaneously oxidized to $Cu^{2+}$ and reduced to elemental copper ($Cu$). This is an example of a disproportionation reaction, where a single substance undergoes both oxidation and reduction.
200. What is the result of the disproportionation of chlorine in the reaction $Cl_2 + 2H_2O \rightarrow HCl + HOCl$?
ⓐ. Chlorine is oxidized to $Cl^-$ and reduced to $Cl_2$
ⓑ. Chlorine is reduced to $Cl^-$ and oxidized to $Cl_2$
ⓒ. Chlorine is oxidized to $Cl^+$ and reduced to $Cl_2$
ⓓ. Chlorine is oxidized to $Cl^-$ and reduced to $Cl_3$
Correct Answer: Chlorine is reduced to $Cl^-$ and oxidized to $Cl_2$
Explanation: In this reaction, chlorine ($Cl_2$) undergoes disproportionation. One chlorine atom is reduced to chloride ions ($Cl^-$), and the other is oxidized to hypochlorite ions ($HOCl$). This is a classic disproportionation reaction.
You’re now on Class 11 Chemistry MCQs – Chapter 8: Redox Reactions (Part 2). The full chapter has 376 MCQs in 4 parts; this section brings the second set of 100 questions. These MCQs strengthen your understanding of oxidation number, types of redox reactions, and identifying oxidizing & reducing agents.
How to practice
- Attempt 10–20 MCQs; check answers instantly with explanations.
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- 👉 Total in chapter: 376 (100 + 100 + 100 + 76)
- 👉 This page: Second set of 100 solved MCQs
- 👉 Next: Proceed to Part 3 for more practice