On immersing an iron nail in ${\text{CuSO}}_4$ solution for few minutes, you will observe

On immersing an iron nail in ${\text{CuSO}}_4$ solution for few minutes, we will observe the colour of solution fades away and the surface of iron nail acquire a reddish brown

Due to iron is more reactive than copper reactivity. $\text{Fe}>\text{Cu}$.

$\underset{Blue}{CuS{O}_{4\left(aq\right)}}+\underset{Brown}{F{e}_{\left(s\right)}}\to \underset{Green}{FeS{O}_{4\left(aq\right)}}+\underset{\mathrm{Re}ddishBrown}{C{u}_{\left(s\right)}}$