(i) Fe3O4 + 4CO → 3Fe + 4CO2

(ii) Cu2O + C → 2Cu + CO

(iii) Cu2+ (aq) + Fe (s) → Cu (s) + Fe2+ (aq)

(iv) Cu2O + 1/2Cu2S → 3Cu + 1/2SO2

Correct Answer: (iv) Cu2O + 1/2Cu2S → 3Cu + 1/2SO2

Explanation: Sulphide ores of certain metals such as Hg, Pb and Cu if heated in the air they bring about the conversion of part of the metal sulphide into oxide or sulphate and then react with the remaining sulphide to give matte SO2. Reducing agent is not used in this process.

Reaction Involved:

2Cu₂​S+3O₂​→2Cu₂O+3SO₂

2Cu₂O+Cu₂​S→6Cu+SO₂