When a glass prism of refracting angle $60^{\circ}$ is immersed in a liquid its angle of minimum deviation is $30^{\circ}$. The critical angle of glass with respect to the liquid medium is :

Question

( A ) $50^{\circ}$
( B ) $42^{\circ}$
( C ) $52^{\circ}$
( D ) $45^{\circ}$