Line.
30. The line perpendicular to point where a ray of light reflects is called the
a. angle of reflection
b. angle of incidence
c. normal
d. law of reflection

c) Normal

Explanation:

Reflection is a phenomenon typical of light wave; it occurs when a ray of light hits the interface between two mediums, and bounces off back into the original medium, at a certain angle.

The direction of the reflected ray is determined by the law of reflection, which states that:

1) The incident ray and the reflected ray, together with the normal to the interface (the perpendicular to the interface), all lie within the same plane

2) The angle of incidence is equal to the angle of reflection:

where

is measured as the angle between the incident ray and the normal to the interface

is measured as the angle between the reflected ray and the normal to the interface