Chemistry - CHEMICAL BONDING Question with Solution | TestHub

The correct statement is (D). The stability order ${\mathrm{Tl}}^{+1}>{\mathrm{In}}^{+1}>{\mathrm{Ga}}^{+1}$ is due to the inert pair effect, where the reluctance of the outermost s-electrons to participate in bonding increases down the group, stabilizing the lower oxidation state.

Let's analyze other options:

A. ${\mathrm{Bi}}^{+3}$ is more stable than ${\mathrm{Bi}}^{+5}$ due to the inert pair effect, not high lattice energy of ${\mathrm{Bi}}^{+5}$.

B. In group 13, the stability of the higher oxidation state (e.g., $+3$) DECREASES on descending the group, while the stability of the lower oxidation state (e.g., $+1$) INCREASES due to the inert pair effect.

C. $\mathrm{PbC}{\mathrm{l}}_4$ is stable, but $\mathrm{Pb}{\mathrm{I}}_4$ does not exist because ${\mathrm{I}}^{-}$ is a strong reducing agent and $\mathrm{P}{\mathrm{b}}^{+4}$ is a strong oxidizing agent, leading to redox reaction, not primarily steric effect.