Aluminium is usually found in +3 oxidation state. In contrast, thallium exists in +1 and +3 oxidation states. This is due to:

Inert pair effect is the prominent character of the p-block element. In this, the high molecular weight element of the group show a lower oxidation state. This is because on going down the group, the shielding effect increases, but d-subshell and f-subshell show poor shielding effect. The high molecular weight members of p-block groups contain d-subshell and f-subshell. Because of this, they show a lower oxidation state. Hence, option D is correct.