To determine the correct order of atomic radii in group 13 elements, we need to consider the trends in atomic size within the group.$\\$Group 13 elements include: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl).$\\$The general trend in a group is that atomic size increases as we move down the group due to the addition of electron shells. However, there are some exceptions due to the presence of d- and f-electrons.$\\$Let's analyze the atomic radii order:$\\$• Boron (B) is the smallest because it is at the top of the group.$\\$• Aluminum (Al) is larger than Boron (B).$\\$• Gallium (Ga) is slightly smaller than Aluminum (Al) due to the poor shielding effect of the 3d electrons, which causes a contraction in size.$\\$• Indium (In) is larger than Gallium (Ga) as expected due to the addition of another electron shell.$\\$• Thallium (Tl) is the largest because it is at the bottom of the group.$\\$Therefore, the correct order of atomic radii is:$\\ B < Ga < Al < In < Tl \\$This corresponds to Option 4.