(a) Group 13 includes all of the elements that are found in the same column as boron. They each have three electrons in their valence shells as a result. All of the other elements in this group, including aluminium, gallium, indium, and thallium, are metals with the exception of boron, which is a non-metal.
(b) Group 13 is made up of all the elements in the same column of the Periodic Table as fluorine, all of which share three electrons in their valence shells.