Question

why does the colur of copper sulphate solution change when an iron nail is kept immersed in it ?

Answer 1

hope this will help u :-
copper sulphate solution changes its color because iron nail dipped in the solution is more reactive then copper sulphate it displaces its molecules. this reaction is called displacement reaction.

Answer 2

 the color of copper sulfate solution change when an iron nail is kept immersed in it because iron displaces copper from its solution and the copper gets deposited over the nail as the copper sulfate solution becomes iron sulfate solution the colour changes from blue to green this is because of displacement reaction between the iron and copper sulfate solution