25. In total internal reflection when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction ?

25. In total internal reflection when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction ?

(a) 180°

(b) 0°

(c) equal to angle of incidence

(d) 90°

Answer :  (d) 90°