Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?

Explanation

When an iron nail is dipped in copper sulphate solution, iron being more reactive than copper, displaces it from its solution, hence the copper sulphate solution loses its colour.
`underset("blue")(CuSO_(4))(aq.)+underset("Grey")(Fe(s))to underset("green")(FeSO_(4))(aq.)+Cu(s)`.