Elements exhibit variable valencies are

Here, the given three elements exhibit variable valencies.

Ex: Copper (Cu) shows Cu(I) in ${\text{Cu}}^{+}$and Cu(II) in ${\text{Cu}}^{2+}$.

Similarly, Iron (Fe) shows Fe (II) in ${\text{Fe}}^{2+}$and Fe (III) in${\text{Fe}}^{3+}$ .

Tin shows Variable valency as Sn²⁺ and Sn⁴⁺.