Answer: Copper(II) oxide reacting with hydrogen to form copper.
- A Magnesium burning in oxygen to form magnesium oxide
- B Iron slowly forming rust in the presence of moist air
- C Copper(II) oxide reacting with hydrogen to form copper
- D Sodium metal reacting vigorously with water to release hydrogen gas
Correct answer: C. Copper(II) oxide reacting with hydrogen to form copper
Explanation: In CuO + H₂ → Cu + H₂O, Cu goes from +2 to 0 (gains electrons); copper oxide is reduced. (Hydrogen is oxidised from 0 to +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.