Question

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

• A. lanthanoid contraction
• B. lattice effect
• C. diagonal relationship
• D. inert pair effect

Answer 1

The correct option is D inert pair effect

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.