Answer: −1.
- A −2
- B 0
- C −1
- D +1
Correct answer: C. −1
Explanation: In peroxides oxygen atoms share a single O–O bond, giving each an oxidation number of −1.
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.