Why does copper deposit when an iron nail is placed in copper sulphate solution?

Correct answer: Iron is more reactive than copper and displaces it

A more reactive metal displaces a less reactive metal from its salt solution. Iron is more reactive than copper, so iron atoms lose electrons and enter solution as Fe²⁺, while Cu²⁺ ions gain electrons and become copper metal on the nail. The net reaction is Fe + CuSO₄ → FeSO₄ + Cu. Thus A is correct; copper does not displace iron, and water or sulphate gas is not responsible.