Blue colour of `CuSO_(4)` solution is discharge slowly when an iron rod is dipped into it. Why?

Explanation

Zinc lies below copper in the electrochemical series and can therefore, release electrons to the `Cu^(2+)` ions. As a result, Zn is oxidised while `Cu^(2+)` ions are reduced. Since the concentration of `Cu^(2+)` ions in the solution decreases, the blue colour of the solution is slowly discharged.
`Zn(s) +Zn^(2+)(aq) to Zn^(2+)(aq) +Cu(s)`