The first thing to take into account is that the product of the slopes of two perpendicular lines lays -1. This means we need the slope of line FG. This slope is given by:
If the slope of FG is 1/2 then the slope "m" of a perpendicular line is given by:
So the perpendicular line must have a slope of -2 and the only option that shows a line with that slope is option C.