The refractive index of the materiel of a prism is $\sqrt{2}$ and the angle of the prism is ${30}^o.$ One of the two refracting surface of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is

• A

  ${30}^o$
• Correct answer
  B

  ${45}^o$
• C

  ${60}^o$
• D

  Zero

Hence, the correct answer is option: 'B'.