Question

why the colour of copper sulphate solution change when an iron nail is dipped in it

Answer 1

the colour of copper sulphate solution changes when an iron nail is dipped into it because iron is more reactive than copper so iron displace the copper from CuSO4 .

Answer 2

this is due displacement of Cu by Fe.

CuSO4 + Fe ------>  FeSO4 + Cu

when an iron nail is dipped in  cuso4(blue colour) the colour of the solutions changes to light green colour

hope it helps.......