Question

Why does the colour of cooper sulphate change when aniron nail is dipped in it?

Answer 1

the colour of copper sulphate changes because iron displaces copper to form iron sulphate.
CuSO4+Fe------->FeSO4+Cu.

Answer 2

when iron nail is dipped in coppersulphate colour is change because iron is more reactive than copper so it displaces copper from coppersulphate and make iron sulphate

CuSO4 + Fe= FeSO4 + Cu
and color of ferrous sulphate is light green