CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 22(b)

Beakers with aluminium and zinc: the pale green colour of the iron sulphate solution fades and the solution becomes colourless, and a greyish-black deposit of iron forms on the strips. Beakers with copper and iron: no change - the solution stays pale green and the strips are unaffected. Reason: aluminium and zinc are more reactive than iron and displace it: $2\text{Al}+3{\text{FeSO}}_4\to {\text{Al}}_2({\text{SO}}_4{)}_3+3\text{Fe}$ and $\text{Zn}+{\text{FeSO}}_4\to {\text{ZnSO}}_4+\text{Fe}$. Copper is less reactive than iron, and iron cannot displace itself, so no reaction occurs in those beakers.