Which of the following oxidation states are the most...

The group IV elements show tetravalency due to shifting of one electrons of $n s$ to the vacant $n p$ orbital. These four orbitals give rise to four $s p^3$ hybrid orbitals. However, $\mathrm{Ge}, \mathrm{Sn}$ and $\mathrm{Pb}$, have a tendency to form divalent as well as tetravalent ions. As the inert pair effect increases from $\mathrm{Ge}$ to $\mathrm{Pb}$, the stability of tetravalent ion decreases and that of divalent ion increases. Thus, $\mathrm{Pb}^{++}$is more stable than $\mathrm{Pb}^{4+}$ and $\mathrm{Sn}^{4+}$ ions is more stable than $\mathrm{Sn}^{2+}$.