Question

why does zinc replaces copper in copper sulphate solution

Answer 1

Zinc displaces copper in copper sulphate solution as zinc is more reactive metal than copper (zinc comes above in reactivity series)
and can displace it
Zn+CuSO4--------ZnSO4+Cu

Answer 2

Heya....
Here you go

According to the reactivity series Zinc is more reactive than copper that is the basic reason behind the displacement of copper from copper Sulphate solution.
Zn+CuSO4-----ZnSO4+Cu