Question

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

Answer 1

hii....
the answer is...
the colour of copper sulphate solution changes when iron nail is dipped in it because the displacement reaction takes place and the iron being more reactive replaces copper from its solution due to which change of colour takes place.

Answer 2

the colour of copper sulphate solution changes because iron is more reactive metal than copper as it displaces it from its aqueous solution