Question

The stability of +1 oxidation state among Al, Ga, In and Tl increases in the sequence:
(A) Tl < In < Ga < Al
(B) In < Tl < Ga < Al
(C) Ga< In < Al < Tl
(D) Al < Ga < In < Tl

Answer 1

Al, Ga, In and Tl are the elements of the same group and the group is boron family. The stability of the +1 oxidation state of these elements can be given by inert pair effect.

Complete step by step solution:
We know that Al, Ga, In and Tl are the elements of the boron family in the periodic table.
- The stability of their +1 oxidation states can be explained by inert pair effect.
- The inert pair effect is the tendency of the two electrons in the valence s-orbital to remain unshared in the formation of bond.
- Inert pair effect can be regarded as the increased stability of the oxidation states that are two less than the group valency for the elements of groups 13,14,15 and 16. Thus, the name suggests that the s-orbital electrons are more difficult to be shared.
- So, we can say that as we go down the group, the stability of the +1 oxidation state increases due to this inert pair effect. So, $T{l^ + }$ is most stable amongst them. The order of their stability can be given as:
$A{l^ + } < G{a^ + } < I{n^ + } < T{l^ + }$

- Thus, we can say that the correct answer of this question is (D)

Note: Note that compounds in lower oxidation states are more ionic and the compounds with higher oxidation states tend to be more covalent. The same trend of stability of +1 oxidation states of elements is noted in group 14,15 and 16.