The refractive index of the material of a prism is $\sqrt 2$and its refracting angle is 30º. One of the refracting surfaces of the prism is made a mirror inwards. A beam of monochromatic light entering the prism from the other face will retrace its path after reflection form the mirrored surface if its angle of incidence on the prism is

Question

( A ) 60$^{\circ}$
( B ) 0$^{\circ}$
( C ) 30$^{\circ}$
( D ) 45$^{\circ}$