Angle of a prism is 30° and its refractive index is $\sqrt{2}$ and one of the surfaces is silvered. At what angle of incidence, a ray should be incident on one surface so that after reflection from the silvered surface, it retraces its path

45°

From the figure, $r_1=30°$

Using snell's law, $i \times \sin i=\mu \sin r_1$

⇒ $\sin \mathrm{i}=(\sqrt{2}) \times \sin 30°$

⇒ i = 45°