Question

why does colour of copper sulphate solution change to light green when iron filling are added ?

Answer 1

When Iron nail (Ferrum) is dipped in Copper sulphate (CuSO4) there takes reaction between them and coppersulphate change its color from blue to light green. This shows Iron is more reactive than Copper, it can replace Copper from CuSO4. CuSO4 is in blue Color and FeSO4 is in light green color.

Answer 2

Because iron is more reactive than copper so it displaces copper from copper sulphate solution