JEE Main 2025 Jan 28 Shift 1, Chemistry Q16: Periodicity In Atomic Properties

Rank the six elements by their first ionisation enthalpy (kJ/mol):

Highest IE${}_1$: Ge. Being the lightest of the listed Group 14 elements, the inert-pair effect is not yet significant, so its most stable oxidation state is $+4$ (as in GeO${}_2$, GeCl${}_4$).

Lowest IE${}_1$: In. Note that IE${}_1$(In) $<$ IE${}_1$(Tl), which looks anomalous but is well known: the poor screening by the intervening $4f^{14}$ and $5d^{10}$ electrons raises the effective nuclear charge on Tl and pushes its IE${}_1$ above that of In. The most stable oxidation state of In is $+3$ (as in In${}_2$O${}_3$, InCl${}_3$); the +1 state exists but is far less common than In(III).

$\therefore$ Most stable oxidation states are $+4$ (Ge) and $+3$ (In), matching option (2).