Question

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

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

Hint:

Down group 13, radii increase, but Ga is smaller than Al due to d-block contraction. Compare covalent or metallic radii for consistency. Check periodic trends for anomalies.

Answer 1

The Correct Option is B

1. Atomic radii generally increase down a group due to additional electron shells.
2. For group 13 (Al, Ga, In, Tl), expect Al<Ga<In<Tl, but Ga's radius is smaller than Al's due to d-block contraction (poor shielding by 3d electrons).
3. Approximate radii: Al (143 pm), Ga (135 pm), In (167 pm), Tl (170 pm).
4. Thus, the order is Ga<Al<In<Tl.
5. Therefore, the correct option is (2) Ga < Al < In < Tl.