Answer: Both oxidation and reduction (disproportionation).
- A Mainly oxidation, since every oxygen atom ends up in O<sub>2</sub>
- B Mainly reduction, since every oxygen atom ends up in H<sub>2</sub>O
- C Both oxidation and reduction (disproportionation)
- D Neither oxidation nor reduction, since the reaction is mainly physical
Correct answer: C. Both oxidation and reduction (disproportionation)
Explanation: In H₂O₂, O is -1. In H₂O, O is -2 (reduction); in O₂, O is 0 (oxidation). The same element (O) is both oxidised and reduced: disproportionation.
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.