# The refractive index of the material of a prism is $\sqrt{2}$ and the angle of the prism is $30^o$. One of the two refracting surfaces 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 reflecting from the silvered surface) if its angle of incidence on the prism is
( A ) $60^o$
( B ) $30^o$
( C ) $45^o$