Find angle of refraction in a medium $(\mu =2)$ . If light is incident in vacuum making angle equal to twice the critical angle.

Question

$(a)\;\sin^{-1} \frac{\sqrt 3}{2} \\ (b)\;\sin ^{-1} \frac{\sqrt 3 }{4} \\ (c)\;\sin ^{-1} \frac{\sqrt 3}{2 \sqrt 2} \\ (d)\;\sin ^{-1} \frac{1}{\sqrt 2} $