Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Because iron is more reactive than copper, it displaces copper from the copper sulphate solution when an iron nail is dipped in the solution. As a result, the copper sulphate solution\’s colour changes from blue to green.

The result is CuSO₄ ( Blue) + Fe → FeSO₄ (Green) + Cu