Answer: 3.
- A 5
- B 3
- C 1
- D 7
Correct answer: B. 3
Explanation: In acidic medium, Mn goes from +7 to +2 (n-factor = 5). In neutral or faintly alkaline medium, MnO₄⁻ is reduced to MnO₂ (Mn +4); n-factor = 7 - 4 = 3.
Electron transfer in a redox reaction: zinc loses electrons (oxidised, acts as reducing agent) and copper(II) ions gain those same electrons (reduced, acts as oxidising agent).
Concept context
Master electron transfer in chemistry: assign oxidation states, balance half-reactions, identify oxidising and reducing agents, and connect redox to everyday reactions.