Final answer:
The angle of reflection of a light ray incident on a plane mirror at 45 degrees with the normal is also 45 degrees, in accordance with the law of reflection.
Step-by-step explanation:
When a light ray is incident on a plane mirror at an angle of 45° with the normal, the angle of reflection is also 45° with the normal. This follows from the law of reflection, which states that the angle of incidence is equal to the angle of reflection. In the given case, both angles are measured relative to the normal, which is the line perpendicular to the surface at the point where the light ray strikes.