CuSO4 will react with elements placed above it in electrochemical series and it would not react with elements places below it in electrochemical series.
∴ CuSO4 reacts with Zn and Fe placed above it. CuSO4 + Fe → FeSO4 + Cu CuSO4 + Zn → ZnSO4 + Cu
∴ CuSO4 does not react with Ag, placed below it. CuSO4 + Ag → no reaction.