Question

what happens when an iron nail is dipped in copper sulphate solution for 20 minutes

Answer 1

As iron is more reactive than copper so it displaces copper from copper sulphate solution which is blue in colour and change into ferrous sulphate that is green  in colour

Answer 2

After 20 minutes...

In this case, iron, being more reactive than copper, will displace it from the solution. That is, ferrous ions or Fe(II) will go into the solution, while curic or Cu(II) will be deposited onto the nail. This cause the solution color tochange from blue to green.

The displacement reaction taking place can e written as :
Fe + CuSO4(aq) == FeSO4 + Cu


Hope you got the answer