JEE Main Redox Reaction Previous Year Questions with Solutions

Redox Reaction Previous Year Questions with Solutions are given here. Redox reactions are oxidation-reduction chemical reactions in which the reactants undergo a change in their oxidation states. The oxidation and reduction reactions always occur simultaneously, so this reaction was named as the redox reaction or Oxidation-Reduction Reaction. The substance getting reduced in a chemical reaction is known as the oxidizing agent, while a substance that is getting oxidized is known as the reducing agent.

This chapter includes topics such as types of redox reactions, oxidation and reduction reactions, oxidising and reducing agents, the reduction potential of half-reaction, balancing redox reactions, etc. This article gives an idea of which type of questions can be expected from the topic redox reaction for JEE. BYJU’S provides accurate solutions that are prepared by our subject matter experts. Students can easily download these solutions in PDF format for free.

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JEE Main Previous Year Solved Questions on Redox Reaction

1. Given : XNa₂HAsO₃ +YNaBrO₃+ZHCl → NaBr + H₃AsO₄ + NaCl

The values of X, Y and Z in the above redox reaction are respectively :

(1) 2, 1, 3

(2) 3, 1, 6

(3) 2, 1, 2

(4) 3, 1, 4

Solution:

The balanced equation is given below.

3Na₂HAsO₃ + NaBrO₃ + 6HCl → NaBr + 3H₃AsO₄ + 6NaCl

The value of X, Y and Z are 3, 1 and 6 respectively.

Hence option (2) is the answer.

2. An alkali is titrated against an acid with methyl orange as an indicator, which of the following is a correct combination?

Solution:

When methyl orange is added to a weak base solution, the solution becomes yellow. When the solution is titrated with a strong acid, after the endpoint, the solution is acidic. So the solution becomes pinkish red.

Hence option (2) is the answer.

3. Consider the following reaction:

xMnO₄^–+ yC₂O₄^2- +zH⁺ → xMn²⁺ + 2yCO₂+(z/2)H₂O

The values of x, y and z in the reaction are respectively :-

(1) 5, 2 and 16

(2) 2, 5 and 8

(3) 2, 5 and 16

(4) 5, 2 and 8

Solution:

The balanced equation is given below.

2MnO₄^–+ 5C₂O₄^2- + 16 H⁺ → 2Mn²⁺ + 10CO₂+8H₂O

The values of x, y and z are 2, 5 and 16, respectively.

Hence option (3) is the answer.

4. Consider the reaction

H₂SO₃(aq) + Sn⁴⁺(aq) + H₂O(l) → Sn²⁺(aq) + HSO₄^–(aq) + 3H⁺(aq)

Which of the following statements is correct?

(1) H₂SO₃ is the reducing agent because it undergoes oxidation

(2) H₂SO₃ is the reducing agent because it undergoes reduction

(3) Sn⁴⁺ is the reducing agent because it undergoes oxidation

(4) Sn⁴⁺ is the oxidizing agent because it undergoes oxidation

Solution:

Oxidation is the loss of electrons during a reaction by a molecule. In the given equation, H₂SO₃ is the reducing agent because it undergoes oxidation.

Hence option (1) is the answer.

5. In which of the following reaction H₂O₂ acts as a reducing agent ?

(1) H₂O₂ + 2H⁺ + 2e^– → 2H₂O

(2) H₂O₂ -2e^– → O₂+2H⁺

(3) H₂O₂ + 2e^– → 2OH^–

(4) H₂O₂ + 2OH^– -2e^– → O₂ + 2H₂O

(1) (1), (3)

(2) (2), (4)

(3) (1), (2)

(4) (3), (4)

Solution:

Reducing agent is an element or compound that loses an electron to an electron recipient in a redox chemical reaction. In (2) and (4) , H₂O₂ acts as a reducing agent.

Hence option (2) is the answer.

6. How many electrons are involved in the following redox reaction?

Cr₂O₇^2- + Fe²⁺ + C₂O₄^2- → Cr³⁺ + Fe³⁺ + CO₂ (Unbalanced)

(1) 3

(2) 4

(3) 5

(4) 6

Solution:

A redox reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron. Chromium and iron are involved in the reaction which is oxidised and reduced. So, a total of 6 electrons are involved in this redox reaction.

Hence option (4) is the answer.

7. Which of the following reactions is an example of a redox reaction ?

(1) XeF₄ + O₂F₂ → XeF₆ + O₂

(2) XeF₂ + PF₅ → [XeF]⁺ PF₆^–

(3) XeF₆ + H₂O → XeOF₄ + 2HF

(4) XeF₆ + 2H₂O → XeO₂F₂ + 4HF

Solution:

In equation (1) Xe undergoes oxidation and oxygen undergoes reduction.

Hence option (1) is the answer.

8. Which of the following is a redox reaction ?

(1) NaCl + KN03 → NaN03 + KC1

(2) CaC204 + 2HC1 → CaCl2 + H2C20,

(3) Mg(OH)2 + 2NH4C1 → MgCl2 + 2NH4OH

(4) Zn + 2AgCN → 2Ag + Zn(CN)2

Solution:

A redox reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron. The oxidation state shows a change only in a reaction between zinc and cyanide.

Hence option (4) is the answer.

9. When KMn0₄ acts as an oxidising agent and ultimately forms [MnO₄^2-, MnO_2, Mn₂O₃ and Mn⁺². Then the number of electrons trans­ferred in each case respectively is

(1) 4, 3, 1, 5

(2) 1, 5, 3, 7

(3) 1,3, 4, 5

(4) 3, 5, 7,1

Solution:

The oxidation number of Mn in KMn0₄, MnO₄^2-, MnO_2, Mn₂O₃ and Mn⁺² 7, 6, 4, 3 and 2 respectively. The number of electrons transferred corresponds to the change in the oxidation number. When KMn0₄ acts as an oxidising agent and ultimately forms MnO₄^2-, MnO_2, Mn₂O₃ and Mn⁺², then the number of electrons transferred in each case are 1,3,4,5 respectively.

Hence option (3) is the answer.

10. For the redox reaction: Zn_(s) + Cu²⁺ (0.1 M)→ Zn⁺ (1M) + Cu_(s) taking place in a cell, E°cell is 1.10 volt. E_cell for the cell will be (2.303 RT / F = 0.0591)

(1) 2.14 V

(2) 1.80 V

(3) 1.07 V

(4) 0.82 V

Solution:

E_cell = E⁰_cell – (0.0591/n) log(1/0.1)

E⁰_cell = 1.10 V

n = 2

E_cell = 1.10 – (0.0591/2) log(10)

= 1.10 – 0.0295

= 1.0705 V

Hence option (3) is the answer.

11. What would happen when a solution of potassium chromate is treated with an excess of dilute nitric acid?

(1) Cr₂O₇^2- and H₂O are formed

(2) Cr₂O₇^2- is reduced to +3 state of Cr

(3) Cr₂O₇^2- is oxidises to +7 state of Cr

(4) Cr³⁺ and Cr₂O₇^2- are formed

Solution:

Dilute HNO₃ is an oxidising agent.

2K₂CrO₄ + 2HNO₃(dil) → K₂Cr₂O₇2KNO₃ + H₂O

CrO₄^2- + 2HNO₃ (dil) → Cr₂O₇^2- + 2NO₃^– + H₂O

Hence option (1) is the answer.

12. Excess of KI reacts with CuSO₄ solution and then Na₂S₂O₃solution is added to it. Which of the statements is incorrect for this reaction?

(1) Cu₂I₂ is reduced

(2) Evolved I₂ is reduced

(3) Na₂S₂O₃is oxidized

(4) CuI₂ is formed

Solution:

2CuSo₂ + 4KI → Cu₂I₂ +2K₂SO₄ + I₂

I₂ +2Na₂S₂O₃ → Na₂S₄O₆ + 2NaI

Here statement (4) is incorrect.

Hence option (4) is the answer.

13. The highest electrical conductivity of the following aqueous solutions is of

(1) 1 M acetic acid

(2) 1 M chloroacetic acid

(3) 1 M fluoroacetic acid

(4) 1 M difluoroacetic acid

Solution:

More the acidity more will be the tendency to release protons. So lighter will be the electrical conductivity. Difluoroacetic acid will be the strongest acid because of the electron-withdrawing effect of two fluorine atoms so as it will show maximum electrical conductivity.

Hence option (4) is the answer.

14. Amount of oxalic acid present in a solution can be determined by its titration with KMnO₄ solution in the presence of H₂SO₄. The titration gives unsatisfactory result when carried out in the presence of HCl because HCl

(1) gets oxidised by oxalic acid to chlorine

(2) furnishes H⁺ ions in addition to those from oxalic acid

(3) reduces permanganate to Mn²⁺

(4) Oxidises oxalic acid to carbon dioxide and water

Solution:

HCl is a strong reducing agent. It reduces permanganate to Mn²⁺.

Hence option (3) is the answer.

15. The oxidation state of chromium in the final product formed by the reaction between KI and acidified potassium dichromate solution is

(1) +4

(2) +6

(3) +2

(4) +3

Solution:

K₂Cr₂O₇ + 7H₂SO₄ + 6KI → Cr₂(SO₄) + 3I₂ + 7H₂O + 4K₂SO₄

Cr get reduced from +6 Oxidation state to +3 oxidation state.

Hence option (4) is the answer.

Also Read:- Redox Reactions