Answer: Mixed: 1/3 Fe2+ and 2/3 Fe3+ (average +8/3).
- A All iron present as Fe2+ throughout the entire compound
- B All iron present as Fe3+ throughout the entire compound
- C Mixed: 1/3 Fe2+ and 2/3 Fe3+ (average +8/3)
- D All iron present as the unusually high Fe4+ oxidation state
Correct answer: C. Mixed: 1/3 Fe2+ and 2/3 Fe3+ (average +8/3)
Explanation: Fe₃O₄ is a mixed oxide: FeO·Fe₂O₃. It contains one Fe²⁺ and two Fe³⁺ per formula unit. Average oxidation state = (2 + 3 + 3)/3 = 8/3 ≈ +2.67.
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.