Study the square grid below. Which line in the square grid is perpendicular to BC?

1. Determine the horizontal and vertical changes for line BC.

From point $B$ to point $C$, the line moves $2$ units to the right and $3$ units down.

2. Determine the required changes for a perpendicular line.

For a line to be perpendicular to $BC$, its horizontal and vertical changes must be swapped, with one direction reversed. It must move $3$ units to the right and $2$ units up (or $3$ units left and $2$ units down).

3. Check the given options to find the perpendicular line.

Checking line $BF$: from point $F$ to point $B$, the line moves $3$ units to the right and $2$ units up. This matches the condition for perpendicularity.