Hi,
When iron nails are dipped in copper sulphate solution, the blue colour of the solution fades away. This is because iron is more reactive than copper. Hence, it will displace copper from copper sulphate forming ferrous sulphate and copper. The chemical equation for the reaction is shown as follows :
CuSO4 (aq) + Fe (s) → FeSO4 (aq) + Cu (s)
Regards