So for this example question, it says predicted charge that a gallium ion would possess. So we know it has a charge because it's using the term ion. Now gallium remember gallium is element symbol is GA. Gallium itself is in Group 3A, or what we known as group 13.
Now remember, in this group it's easier to lose electrons because most of the elements in this group are metals, and it's easier for them to lose 3 electrons in order to be like the nearest noble gas South. Here this group 38 normally tends to be plus three in terms of charge. Because of this, option C would be our correct answer.