When an iron nail is placed in a blue copper sulphate solution, a reddish-brown copper coating forms on the nail and the solution turns pale green. What causes both changes?

Correct answer: Iron displaces copper from copper sulphate and forms iron sulphate.

Iron is more reactive than copper, so it displaces copper from copper sulphate solution. The reaction is \(\mathrm{Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)}\). The released copper deposits as a reddish-brown coating on the nail, while the iron sulphate formed makes the solution pale green. Rusting in option B is a different process and does not produce a copper coating.