The wave length of light in 1st liquid is $2500 \;\mathring{A}$, and that in 2nd liquid is $5000\; \mathring{A}$, What is the critical angle of 1st liquid with respect to 2nd liquid.

Question

$(a)\;60^{\circ} \\ (b)\;45^{\circ} \\ (c)\;30^{\circ} \\ (d)\;90^{\circ}$