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 :

Statement I: In group 13, the stability of +1 oxidation state increases down the group.

This is correct due to the inert pair effect. As we go down the group, the $$ns^2$$ electrons become less available for bonding, making the +1 state more stable. Tl predominantly shows +1 state. ✓

Statement II: The atomic size of gallium is greater than that of aluminium.

Due to d-block contraction (poor shielding by 3d electrons), Ga has a smaller atomic radius than Al. The actual order is Al (143 pm) > Ga (135 pm). Statement II is incorrect. ✗

The correct answer is Option (4): Statement I is correct but Statement II is incorrect.