Three aqueous solutions are taken in the beakers labeled X, Y, Z. When kiran add the iron nails to beaker X, it changes its colour blue to green. and Ravi added Zn metal to Y then he can’t observe any change. Santhosh added name Zn metal to beaker Z. Then green colour solution fade out by forming a black solid at bottom of the beaker. Then imagine the three solutions in X, Y and Z.

When kiran added the iron nails to beaker X it changes its colour blue to green. That means according to metal activity series iron metal displaces the metal present in the X solution. So from given four options that X solution must be  ${\text{CuSO}}_4$. Ravi added zinc metal to Y then he can’t observe any change, that means no reaction occur because the metal present in the Y solution is more reactive than zinc or the metal present in the solution also zinc. Santhosh added zinc metal to beaker Z, then green colour solution fade out by forming black solid at bottom of the beaker. That means displacement reaction occur so the metal present in the solution is less reactive than zinc. So finally X solution is  ${\text{CuSO}}_4$, Y solution  ${\text{ZnSO}}_4$ and Z solution is ${\text{FeSO}}_4$.