Question

The correct order of atomic radii of Al, Ga, In, Tl is

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

Hint:

D-block contraction causes Ga to have a smaller radius than Al despite being below it in the group.

Answer 1

The Correct Option is B

Atomic radii generally increase down the group. However, due to poor shielding by d-electrons in Ga (group 13), its radius becomes slightly smaller than expected.
Therefore, the correct order is: Ga<Al<In<Tl
- Ga<Al (due to d-block contraction)
- In<Tl (normal increase down the group)