Question

The correct order of atomic radii in group $13$ elements is _________.

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

Answer 1

Answer: (D)

The correct order of atomic radii in group $13$ elements is:

$B\left(\text{85 pm}\right)<Ga\left(\text{135 pm}\right)<Al\left(\text{143 pm}\right)<In\left(\text{167 pm}\right)<Tl\left(\text{170 pm}\right)$.

On moving down the group, the atomic radius increases from boron to thallium. The atomic radius of Ga is less than that of Al. Ga has 10 d electrons which do not screen the nuclear charge in an effective manner and hence electrons in the outermost shell of Ga experience more force of attraction towards the nucleus than Al. This results in a decrease in atomic radius.

Hence, option C is correct.