Answer: +6.
- A +3
- B +4
- C +6
- D +7
Correct answer: C. +6
Explanation: K₂Cr₂O₇: 2(+1) + 2(Cr) + 7(-2) = 0. 2Cr = 14 - 2 = 12. 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.