JEE Main 2025 Apr 7 Shift 2, Chemistry Q19: Group13 Elements: The Boron Family

Due to the inert pair effect, heavier p-block elements like thallium show increasing stability of the lower oxidation state (+1) relative to the group oxidation state (+3) down the group. Consequently Tl${}^{+}$ is more stable than Tl${}^{3+}$ (D), and Tl${}^{3+}$ readily gains electrons to revert to the more stable Tl${}^{+}$ state, making Tl${}^{3+}$ a powerful oxidising agent (A).

Aluminium, being lighter, does not show a significant inert pair effect, so its +3 state is the stable one; Al${}^{3+}$ has a very negative reduction potential, meaning it strongly resists being reduced back to the metal, so it does not get reduced easily (B), and along with Tl${}^{+}$ it counts among the highly stable species (E).

Statement (C) incorrectly groups Tl${}^{3+}$ with Al${}^{3+}$ as "very stable," but Tl${}^{3+}$ is actually unstable relative to Tl${}^{+}$, so (C) is false.

$\therefore$ (A), (B), (D) and (E) are correct.