Four test tubes were taken and marked A,B,C and D respectively. 2 ml of solution of ${\text{Al}}_2{\left({\text{SO}}_{\text{4}}\right)}_3$ in water was filled in each of the four test tubes, a clean piece of metal Zn was placed in test tube, A, a clean iron nail was put in test tube B, Clean copper wire was placed in test tube C and a clean  aluminium wire was placed in test tube D. It was observed that no change occurred in any of the test tubes. The correct inference drawn is