Answer: +6.
- A +6
- B +10
- C +4
- D +5
Correct answer: A. +6
Explanation: CrO5 has two O22− (−1 each O) and one O2−; Cr + 4(−1) + (−2) = 0 gives Cr = +6.
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.