A ray of light passing through the centre of curvature of a concave mirror is reflected by the mirror at

When a ray of light passes through the center of curvature of a concave mirror, it reflects back on itself and retraces its path. Therefore, the angle of incidence is equal to the angle of reflection, and both angles are measured with respect to the normal, which is a line perpendicular to the surface of the mirror at the point of incidence. Since the ray of light is passing through the center of curvature, it is hitting the mirror at a right angle to the normal, which means that the angle of incidence is 0 degrees. According to the law of reflection, the angle of reflection is also 0 degrees, so the ray of light is reflected back on itself in the same direction that it came from. Therefore, the correct answer is 0 degrees.