The correct order of atomic radii in group 13 elements is

Solution & Explanation

\textbf{Answer:} (D) $\text{B}<\text{Ga}<\text{Al}<\text{In}<\text{Tl}$. \textbf{Solution:} Approximate atomic radii (in pm): $\text{B}85$, $\text{Ga}135$, $\text{Al}143$, $\text{In}167$, $\text{Tl}170$. Gallium is smaller than aluminium because the poor shielding by the intervening $3d$ electrons increases the effective nuclear charge on Ga. Hence the order is $\text{B}<\text{Ga}<\text{Al}<\text{In}<\text{Tl}$.