A ray of light is incident normally on one face ${30}^0-{60}^0-{90}^0$ prism of refractive index ${\mu }_p=\frac{5}{3}$ immersed in water of refractive index ${\mu }_m=\frac{4}{3}$ as shown in the 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 the refractive index of water is increased to $n>\frac{5}{2\sqrt{3}}$ by dissolving some substance.

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