Question

When an incident angle becomes equal to refracted angle?

Answer 1

When the incident angle stricks the mirror at pole then it is equal to refracted angle

Answer 2

When light strikes an interface with an angle of incidence equal to the critical angle, the angle of refraction equals 90 degrees. For any larger angle of incidence, the angle of refraction is not defined (since its sine becomes greater than 1.0, according to Snell's Law), and no light can pass over the interface.