CBSE Class 10 Science 2019 · Paper 31/1/1/C · Question 23

(a) Test tube II (copper). Copper is less reactive than iron, so it cannot displace iron from ferrous sulphate; no reaction takes place and the solution stays pale green, like the solution in test tube I. (b) Test tubes III (zinc) and IV (aluminium). Zinc and aluminium are more reactive than iron and displace it: $\text{Zn}+{\text{FeSO}}_4\to {\text{ZnSO}}_4+\text{Fe}$ and $2\text{Al}+3{\text{FeSO}}_4\to {\text{Al}}_2({\text{SO}}_4{)}_3+3\text{Fe}$. The colourless zinc and aluminium sulphates replace the pale green ferrous sulphate, so the colour fades, and the iron set free is deposited as a black mass on the metal.