A Ray of light passing through the centre of curvature of a concave mirror is incident on its reflecting surface . What is the angle of incidence and angle of reflection of this ray. 

The ray passing through the centre of curvature and strikes the curved reflecting surface makes an angle Zero degree with the normal or 90 degree with the tangent at the point it strikes. This happens because the ray is coming from the center of the sphere of which this curved mirror is the part and in case of circle normal at a point always passes through the centre of the circle. Since the angle of incidence is 0 the angle of reflection is also 0 degree and this ray retraces its path.