Answer: Cu2+ + Cu → 2Cu+.
- A 2H2O2 → 2H2O + O2
- B Cu2+ + Cu → 2Cu+
- C Cl2 + 2NaOH → NaCl + NaOCl + H2O
- D 2MnO4- + 5H2C2O4 → 2Mn2+ + 10CO2 + 8H2O
Correct answer: B. Cu2+ + Cu → 2Cu+
Explanation: Cu²⁺ (OS +2) + Cu (OS 0) → 2Cu⁺ (OS +1). The higher and lower oxidation state of the same element combine to give an intermediate oxidation state. This is comproportionation.
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.