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

Normally, atomic radii increase down a group. However, in Group 13, there is an anomaly between $\text{Al}$ and $\text{Ga}$. Gallium ($\text{Ga}$) comes after the filling of $3d$ orbitals. The $d$ electrons provide poor shielding, which leads to a higher effective nuclear charge on the outer electrons of $\text{Ga}$, causing its radius to be slightly smaller than that of $\text{Al}$.Order: $\text{B}<\text{Ga}<\text{Al}<\text{In}<\text{Tl}$.