A ray of light is incident normally an one face of  $30°-60°-90°$ prism of refractive index $\frac{5}{3}$ immersed in water of refractive index  $\frac{4}{3}$ as shown in figure.

The exit angle ${\theta }_2$  of the ray is  ${\sin }^{-1}\left(\frac{5}{8}\right)$

The exit angle  ${\theta }_2$ of the ray is ${\sin }^{-1}\left(\frac{5}{4\sqrt{3}}\right)$

Total internal reflection at point P ceases if refractive index of water is increased to  $\frac{5}{2\sqrt{3}}$ by dissolving some substance

Total internal reflection at point P ceases if refractive index of water is increased to  $\frac{5}{6}$ by dissolving some substance