The increasing order of the atomic radii of the following elements is :
(a) C (b) O (c) F(d) Cl ( e) Br

Options

A. `B lt Ga lt Al lt Tl lt In`
B. `B lt Al lt Ga lt In lt Tl`
C. `B lt Al lt In lt Ga lt Tl`
D. `B lt Ga lt Al lt In lt Tl`

Answer

D

Explanation

The atomic radii as well as ionic radii increases on moving down the group 13 elements because of the successive addition of one extra shell of electrons.
However, there is an anomaly at gallium in case of atomic radii. Atomic radii of Ga is lesser as compared to Al. Gallium (Ga) with electronic configuration, `[Ar]_(18)3d^(10)4s^(2)4p^(1)` has an extra d-electrons which do not screen the nucleus effectively. Consequentl, electrons of Ga are more attracted by nucleus. Thus, the increasing order of atomic radii of the group 13 elements is B (85 pm) `lt` Ga (135 pm) `lt` Al (143 pm) `lt` In (167 pm) `lt` Tl (170 pm).