Answer: HCl (specifically H+).
- A Zn, the metal that is itself oxidised in this reaction
- B H<sub>2</sub>, the gas that is itself the reduction product here
- C HCl (specifically H+)
- D Cl-, the spectator ion that does not change oxidation state
Correct answer: C. HCl (specifically H+)
Explanation: H⁺ (from HCl) is reduced: 2H⁺ + 2e⁻ → H₂. Since H⁺ accepts electrons, it is the oxidising agent. Zn is oxidised (reducing agent).
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.