Given below are two statements:
Statement I: In group 13, the stability of +1 oxidation state increases down the group.
Statement II : The atomic size of gallium is greater than that of aluminium.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 3 steps

Two things to remember here: the inert pair effect, and gallium being smaller than aluminium.

1. Statement I. Going down group 13, the ns² pair holds on more tightly and stays out of bonding. This is the inert pair effect. So the +1 state grows more stable down the group: thallium is more stable as Tl⁺ than as Tl³⁺. Statement I is correct.
2. Statement II. Gallium comes right after the first transition series, so it has ten 3d electrons. These d electrons shield the nucleus poorly. The outer electrons feel a larger effective nuclear charge and are pulled closer.

   Element	Atomic radius	Electrons below the valence shell
   Al	143 pm	no d electrons
   Ga	135 pm	ten 3d electrons, poor shielding

3. So. Gallium is smaller than aluminium, so Statement II is incorrect. Statement I is correct and Statement II is incorrect, which is option (b).

The idea to keep. In group 13, size does not rise steadily from Al to Ga because the 3d electrons shield poorly. Heavier members prefer the lower oxidation state because of the inert pair effect.

Answer from the NTA final answer key. Solution by PrepWiser.