Choose the correct stability order of group 13 elements in their $$+1$$ oxidation state.

We need to find the correct stability order of Group 13 elements in their $$+1$$ oxidation state.

Understand the Inert Pair Effect

Group 13 elements have the electronic configuration $$ns^2 np^1$$. They can show $$+3$$ and $$+1$$ oxidation states. The stability of the $$+1$$ oxidation state depends on the inert pair effect, where the $$ns^2$$ electron pair becomes reluctant to participate in bonding as we go down the group.

Trend down the group

As we move down Group 13:

- Al: Almost always shows $$+3$$ state. The $$+1$$ state is highly unstable.

- Ga: $$+1$$ state is slightly more stable than Al due to poor shielding by the $$3d$$ electrons, but still predominantly $$+3$$.

- In: $$+1$$ state becomes more stable. Inert pair effect is more pronounced.

- Tl: $$+1$$ state is the most stable oxidation state. Tl(I) compounds like TlCl are more stable than Tl(III) compounds. The inert pair effect is strongest here due to poor shielding by $$4f$$ and $$5d$$ electrons.

Write the stability order

The stability of the $$+1$$ oxidation state increases going down the group:

$$Al < Ga < In < Tl$$

The correct answer is Option A: $$Al < Ga < In < Tl$$.