Question

If a ray is incident on a plane mirror perpendicular to its surface, what are angle of incidence and angle of
reflection and why?​

Answer 1

If a ray is incident perpendicularly on a plane mirror then the angle of incidence is 90° because the ray becomes the normal at that point and the angle between normal and plane mirror is 90°.

We know that angle of incidence = angle of reflection (Laws of reflection)

Therefore, angle of incidence = angle of reflection = 90°.