Why a ray of light through centre of curvature if incident on a plane mirror, reflects back with the same path?

A ray of light falling normal to the mirror returns along the same path.Why?

State Huygens' principle and use it to describe the process of reflection of a parallel beam of light incident on a plane mirror obliquely with the help of a labelled diagram.Prove that the angle of incidence is equal to the angle of reflection.

When an object is placed beyond centre of curvature of a concave mirror, the image is formed:

What is the angle of reflection, when a ray of light is incident normally on a plane mirror?

What are the advantage of total reflecting prism over a plane mirror?

What is curvature of a mirror? What is its value for plane mirror?