Which element has the highest ionization energy?B, Al, Ga, In

BORON

Ionization energy decreases down the group and going from left to right the period,

Luckily you have the elements from the same group that is Group III A also called boron family,

The position of Elements in this group are

so keeping rules in mind the first element in the group has highest I.E. that is boron

i think it's c. i'm not sure but i think so.

the answer your looking for is c).