An iron nail is kept in a blue copper sulphate solution for some time. A reddish-brown coating forms on the nail and the solution turns light green. Which statement about this change is correct?

Correct answer: This is a displacement reaction in which iron displaces copper from its salt solution.

Iron is more reactive than copper, so it displaces copper from copper sulphate solution. Light-green iron(II) sulphate forms, while reddish-brown copper is deposited on the nail: \(\mathrm{Fe + CuSO_4 \rightarrow FeSO_4 + Cu}\). In a combination reaction, reactants generally form one product; here, iron(II) sulphate and copper are two products.