Question

The stability of +1 oxidation state increases in the sequence .

• A. In < Tl < Ga < Al
• B. Al < Ga < In < Tl
• C. Ga < In < Al < Tl
• D. Tl < In < Ga < Al

Hint:

For Group 13, 14, and 15 elements, the lower oxidation state (Group state - 2) always becomes more stable as you go down the group due to the Inert Pair Effect.

Answer 1

The Correct Option is B

Concept:
The elements Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl) belong to Group 13 of the periodic table. These elements have a general outer electronic configuration of ns² np¹. While the expected oxidation state is +3 (by losing all three valence electrons), a phenomenon known as the Inert Pair Effect becomes prominent as we move down the group.

As the atomic size increases down the group, the s-orbital electrons (ns²) are held more tightly by the nucleus due to poor shielding by the intervening d and f electrons. Consequently, these s-electrons become "inert" and do not easily participate in bond formation.

Because the s-electrons become increasingly difficult to remove as we go down the group:

• The stability of the +3 oxidation state decreases.
• The stability of the +1 oxidation state (where only the p¹ electron is lost) increases.

For Thallium (Tl), the +1 state is even more stable than the +3 state. Therefore, the sequence of increasing stability for the +1 oxidation state is:

Al < Ga < In < Tl