The correct angle between the incident and reflected rays when a ray of light is incident normally on a plane mirror is 0°. When a ray of light falls normally on a plane mirror, it means that the incident ray is perpendicular to the surface of the mirror. According to the laws of reflection, the angle of incidence is always equal to the angle of reflection. In this case, since the incident angle is 90°, the reflected angle will also be 90°. However, since the incident ray is perpendicular to the mirror, the angle between the incident and reflected rays is 0°.

To clarify the other options:

- Option 1: 180° - This would be the case if the ray of light was reflected back in the opposite direction, but in this case, the reflection occurs on the same side of the mirror. Therefore, this option is incorrect.

- Option 2: 90° - This would be the correct angle if the incident ray was at an angle to the surface of the mirror, but in the given scenario, the incident ray is normal to the mirror. Therefore, this option is incorrect.

- Option 3: 45° - This would be the angle if the plane mirror was at an angle to the incident ray,