Chapter 7: Redox Reactions Assertion-Reason Questions | chemistry Class 11 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): In the reaction 2Mg(s) + O2(g) → 2MgO(s), magnesium is oxidised. Reason (R): Oxidation, in the classical sense, involves the addition of oxygen to a substance.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Oxidation and reduction always occur simultaneously in a redox reaction. Reason (R): The electrons lost by the reducing agent must be gained by the oxidising agent in the same reaction.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): The oxidation number of fluorine is always -1 in all its compounds. Reason (R): Fluorine is the most electronegative element and cannot exhibit any positive oxidation state.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): The decomposition of calcium carbonate (CaCO3 → CaO + CO2) is not a redox reaction. Reason (R): In this reaction, none of the elements undergo a change in their oxidation numbers.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): Fluorine cannot displace other halogens from their halide salts in aqueous solution. Reason (R): Fluorine attacks water itself, oxidising it to O2, so aqueous halide solutions cannot be used with F2.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): The oxidation number of hydrogen in NaH is -1. Reason (R): Hydrogen bonded to a non-metal always has an oxidation number of -1.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): In the Daniell cell, the zinc electrode is the anode. Reason (R): Oxidation takes place at the anode, and zinc is oxidised to Zn2+ ions in the Daniell cell.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): ClO4- does not undergo disproportionation. Reason (R): In ClO4-, chlorine is in its highest oxidation state (+7) and cannot be further oxidised.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 9

Logic Check

Assertion (A): A negative standard electrode potential (E°) for a redox couple means it is a stronger reducing agent than the H+/H2 couple. Reason (R): A more negative E° indicates a lesser tendency to lose electrons compared to the standard hydrogen electrode.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): In the electrochemical series, zinc is placed above copper because zinc can displace copper from copper sulphate solution. Reason (R): Zinc has a more negative standard electrode potential than copper, indicating a greater tendency to lose electrons.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 11

Logic Check

Assertion (A): The oxidation number of oxygen in H2O2 is -1. Reason (R): In peroxides, the two oxygen atoms are directly linked to each other, and each is assigned an oxidation number of -1.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): The concept of oxidation number is described as a bookkeeping device. Reason (R): In covalent compounds, the electron pair is assumed to be completely transferred to the more electronegative atom, even though in reality the transfer is only partial.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): Br2 can displace iodide ions from KI solution but cannot displace chloride ions from KCl solution. Reason (R): Br2 is a stronger oxidising agent than I2 but a weaker oxidising agent than Cl2.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): In the Daniell cell, electrons flow from the copper electrode to the zinc electrode through the external wire. Reason (R): Zinc is oxidised at the anode and releases electrons, which travel through the external circuit to the cathode.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): The decomposition of H2O2 (2H2O2 → 2H2O + O2) is a disproportionation reaction. Reason (R): Oxygen in H2O2 is in the -1 oxidation state, which is intermediate between -2 (in H2O) and 0 (in O2), so it is simultaneously oxidised and reduced.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): Alkali metals displace hydrogen from cold water but not from dilute acids. Reason (R): Alkali metals are very strong reducing agents with highly negative standard electrode potentials.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 17

Logic Check

Assertion (A): The fractional oxidation state of iron in Fe3O4 is +8/3. Reason (R): Fe3O4 is a mixed oxide containing both Fe(II) and Fe(III) in the ratio 1:2, and the fraction +8/3 represents the true oxidation state of each iron atom.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): In the Oxidation Number Method of balancing redox reactions, the increase in oxidation number is made equal to the decrease in oxidation number. Reason (R): This equality reflects the conservation of electrons: the electrons lost by the reducing agent equal the electrons gained by the oxidising agent.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): When a strip of copper is placed in zinc sulphate solution, no visible reaction occurs. Reason (R): Copper has a more positive standard electrode potential than zinc, meaning copper is a weaker reducing agent and cannot displace zinc from its salt.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): The reaction N2(g) + O2(g) → 2NO(g) is classified as a combination redox reaction. Reason (R): Both reactants are in the elemental state (oxidation number 0), and in the product NO, nitrogen has oxidation number +2 and oxygen has -2.

Reasoning Options

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Chapter sections

Chapter 7: Redox Reactions | Assertion-Reason

Assertion (A): In the reaction 2Mg(s) + O2(g) → 2MgO(s), magnesium is oxidised. Reason (R): Oxidation, in the classical sense, involves the addition of oxygen to a substance.

Assertion (A): Oxidation and reduction always occur simultaneously in a redox reaction. Reason (R): The electrons lost by the reducing agent must be gained by the oxidising agent in the same reaction.

Assertion (A): The oxidation number of fluorine is always -1 in all its compounds. Reason (R): Fluorine is the most electronegative element and cannot exhibit any positive oxidation state.

Assertion (A): The decomposition of calcium carbonate (CaCO3 → CaO + CO2) is not a redox reaction. Reason (R): In this reaction, none of the elements undergo a change in their oxidation numbers.

Assertion (A): Fluorine cannot displace other halogens from their halide salts in aqueous solution. Reason (R): Fluorine attacks water itself, oxidising it to O2, so aqueous halide solutions cannot be used with F2.

Assertion (A): The oxidation number of hydrogen in NaH is -1. Reason (R): Hydrogen bonded to a non-metal always has an oxidation number of -1.

Assertion (A): In the Daniell cell, the zinc electrode is the anode. Reason (R): Oxidation takes place at the anode, and zinc is oxidised to Zn2+ ions in the Daniell cell.

Assertion (A): ClO4- does not undergo disproportionation. Reason (R): In ClO4-, chlorine is in its highest oxidation state (+7) and cannot be further oxidised.

Assertion (A): A negative standard electrode potential (E°) for a redox couple means it is a stronger reducing agent than the H+/H2 couple. Reason (R): A more negative E° indicates a lesser tendency to lose electrons compared to the standard hydrogen electrode.

Assertion (A): In the electrochemical series, zinc is placed above copper because zinc can displace copper from copper sulphate solution. Reason (R): Zinc has a more negative standard electrode potential than copper, indicating a greater tendency to lose electrons.

Assertion (A): The oxidation number of oxygen in H2O2 is -1. Reason (R): In peroxides, the two oxygen atoms are directly linked to each other, and each is assigned an oxidation number of -1.

Assertion (A): The concept of oxidation number is described as a bookkeeping device. Reason (R): In covalent compounds, the electron pair is assumed to be completely transferred to the more electronegative atom, even though in reality the transfer is only partial.

Assertion (A): Br2 can displace iodide ions from KI solution but cannot displace chloride ions from KCl solution. Reason (R): Br2 is a stronger oxidising agent than I2 but a weaker oxidising agent than Cl2.

Assertion (A): In the Daniell cell, electrons flow from the copper electrode to the zinc electrode through the external wire. Reason (R): Zinc is oxidised at the anode and releases electrons, which travel through the external circuit to the cathode.

Assertion (A): The decomposition of H2O2 (2H2O2 → 2H2O + O2) is a disproportionation reaction. Reason (R): Oxygen in H2O2 is in the -1 oxidation state, which is intermediate between -2 (in H2O) and 0 (in O2), so it is simultaneously oxidised and reduced.

Assertion (A): Alkali metals displace hydrogen from cold water but not from dilute acids. Reason (R): Alkali metals are very strong reducing agents with highly negative standard electrode potentials.

Assertion (A): The fractional oxidation state of iron in Fe3O4 is +8/3. Reason (R): Fe3O4 is a mixed oxide containing both Fe(II) and Fe(III) in the ratio 1:2, and the fraction +8/3 represents the true oxidation state of each iron atom.

Assertion (A): When a strip of copper is placed in zinc sulphate solution, no visible reaction occurs. Reason (R): Copper has a more positive standard electrode potential than zinc, meaning copper is a weaker reducing agent and cannot displace zinc from its salt.

Assertion (A): The reaction N2(g) + O2(g) → 2NO(g) is classified as a combination redox reaction. Reason (R): Both reactants are in the elemental state (oxidation number 0), and in the product NO, nitrogen has oxidation number +2 and oxygen has -2.

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