Redox Equilibrium is a Class 11 Chemistry chapter that carries about 2.5% of the Chemistry questions in NEET. Practise it with 38 questions covering 2 topics, each with an explanation.
Sample questions on Redox Equilibrium with answers
8 questions from the practice bank, spread across the chapter's topics. The full set is in the app.
Question 1: Electrochemical Series and Redox Titrations
In a redox titration using potassium permanganate (KMnO4), the appearance of a persistent pink color indicates:
- A the start of the reaction
- B the endpoint of the titration
- C that no reaction has occurred
- D that the solution is basic
Answer: B. the endpoint of the titration
Why: KMnO4 acts as a self-indicator; a persistent faint pink color appears at the endpoint once all the reducing agent has been consumed and excess KMnO4 remains unreacted.
Question 2: Oxidation Number and Balancing Redox Reactions
The oxidation numbers of phosphorus in H₃PO₃ and H₃PO₄ are respectively:
- A +5 and +5
- B +5 and +3
- C +3 and +5
- D +3 and +3
Answer: C. +3 and +5
Why: 3(+1) + x + 3(−2) = 0 and 3(+1) + x + 4(−2) = 0.
Question 3: Electrochemical Series and Redox Titrations
In the electrochemical (activity) series, a metal higher up the series compared to another metal is generally:
- A a weaker reducing agent
- B a stronger reducing agent, more easily oxidized
- C less reactive
- D unable to displace other metals
Answer: B. a stronger reducing agent, more easily oxidized
Why: Metals higher in the electrochemical series have a greater tendency to lose electrons (be oxidized), making them stronger reducing agents capable of displacing lower metals from their salt solutions.
Question 4: Oxidation Number and Balancing Redox Reactions
In the reaction 5I⁻ + IO₃⁻ + 6H⁺ → 3I₂ + 3H₂O, iodine undergoes:
- A comproportionation (oxidation and reduction of two different forms to the same product)
- B no change in oxidation state
- C disproportionation
- D only oxidation
Answer: A. comproportionation (oxidation and reduction of two different forms to the same product)
Why: I⁻ (−1) and IO₃⁻ (+5) both give I₂ (0).
Question 5: Electrochemical Series and Redox Titrations
The standard electrode potential of the standard hydrogen electrode (SHE) is taken as:
- A +1.00 V
- B −1.00 V
- C 0.00 V
- D +0.34 V
Answer: C. 0.00 V
Why: SHE is the reference against which all other electrode potentials are measured.
Question 6: Oxidation Number and Balancing Redox Reactions
The oxidation number of manganese in K₂MnO₄ is:
- A +7
- B +6
- C +4
- D +2
Answer: B. +6
Why: 2(+1) + x + 4(−2) = 0, so x = +6.
Question 7: Electrochemical Series and Redox Titrations
A redox reaction is spontaneous under standard conditions when:
- A E°cell is zero
- B E°cell is positive
- C ΔG° is positive
- D E°cell is negative
Answer: B. E°cell is positive
Why: ΔG° = −nFE°cell.
Question 8: Oxidation Number and Balancing Redox Reactions
The average oxidation number of iron in Fe₃O₄ is:
- A +3
- B +4
- C +2
- D +8/3
Answer: D. +8/3
Why: 3x + 4(−2) = 0, so x = 8/3 (a mixture of Fe²⁺ and Fe³⁺).
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