Answer: +2.
- A +2
- B +6
- C −2
- D +2.5
Correct answer: A. +2
Explanation: 2(+1) + 2S + 3(−2) = 0 gives 2S = +4, so the average oxidation number of S is +2.
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.