Answer: −1.
- A +1
- B −1
- C 0
- D +2
Correct answer: B. −1
Explanation: In metal hydrides hydrogen is more electronegative than the metal, so H carries an oxidation number of −1.
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.