Answer: -2.
- A +2
- B -1
- C -2
- D 0
Correct answer: C. -2
Explanation: Oxygen has an oxidation state of -2 in most compounds (except peroxides where it is -1, and OF₂ where it 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.