If a point is located below the principal axis of a spherical mirror, what sign is assigned to its perpendicular distance according to the sign convention for spherical mirrors?

The correct option is Negative.

According to the Cartesian Sign Convention for spherical mirrors:

1. The principal axis of the mirror is taken along the X-axis, and the pole (P) of the mirror is taken as the origin.

2. Distances measured perpendicular to and above the principal axis (along the positive Y-axis) are taken as positive (+).

3. Distances measured perpendicular to and below the principal axis (along the negative Y-axis) are taken as negative (-).

Since the given point is located below the principal axis, its perpendicular distance is measured downward along the negative Y-axis direction, and therefore, a negative sign is assigned to it.