A transparent solid cylindrical rod has a refractive index of $\frac{2}{\sqrt{3}}$. It is surrounded by air. A light ray is incident at the mid point of one end of the rod as shown in the figure. The incident angle $\theta$ for which the light ray grazes along the wall of the rod is <br>

Question

https://clay6.com/mpaimg/962_a.jpg

( A ) $\sin^{-1} (\frac{\sqrt{3}}{2})$
( B ) $\sin^{-1} (\frac{1}{2})$
( C ) $\sin^{-1} (\frac{2}{\sqrt{3}})$
( D ) $\sin^{-1} (\frac{1}{\sqrt{3}})$