A rectangular glass slab $A B C D$ of refractive index $\mu_{1}$, is immersed in water of refractive index $\mu_{2}\left(\mu_{1}>\mu_{2}\right) . \mathrm{A}$ ray of light is incident at the surface $A B$ of the slab as shown. The maximum value of the angle of incidence $\alpha_{\max }$, such that the ray comes out only from the other surface $C D$ is given by
(a) $\sin ^{-1}\left[\left(\frac{\mu_{1}}{\mu_{2}}\right) \cos \left(\sin ^{-1} \frac{\mu_{1}}{\mu_{1}}\right)\right]$
(b) $\sin ^{-1}\left(\frac{\alpha_{2}}{\alpha_{1}}\right)$
(c) $\sin ^{-1}\left[\alpha_{1} \cdot \cos \left(\sin ^{-1} \frac{1}{\alpha_{2}}\right)\right]$
(d) $\left[\sin ^{-1} \frac{\alpha_{1}}{\alpha_{2}}\right]$