A prism of angle $$75^{o}$$ and refractive index $$\sqrt{3}$$ is coated with thin film of refractive index 1.5 only at the back exit surface. To have total internal reflection at the back exit surface the incident angle must be______.
($$\sin 15^{o}$$ = 0.25 and $$\sin 25^{o}$$ = 0.43)

A

$$15^{o}$$

B

between $$15^{o}$$ and $$20^{o}$$

C

$$< 15^{o}$$

D

$$> 25^{o}$$