(a) All the elements are in the same boron column (group 13). Thus, they have three electrons in their valence shells. Besides, non-metallic boron, all other elements (i.e., aluminum, gallium, indium and thallium) in this group are metals.
(b) All substances in the same column of the Periodic Table as fluorine have three identical electrons in their valence shell and all belong to the thirteenth group.