Four test tubes marked I, II, III and IV were taken. $20\mathrm{ml}$ of ${\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3$ solution in water was poured in each of the test tubes. A piece of zinc metal was placed in test tube I, an iron nail was put in test tube II, copper turnings were put in test tube III and a clean aluminium strip was placed in test tube IV. No change was observed in any of the test tubes. The correct inference drawn is