A ray of light is incident from air on a surface of medium at an angle of $60^{\circ}$. The angle of refraction in the medium is $ 30^{\circ}$ what will be the velocity of light in the medium.

Question

$(a)\;2.62 \times 10^{8}\;m/s \\ (b)\;1.26 \times 10^8\;m/s \\ (c)\;4.21 \times 10 ^8\;m/s \\ (d)\;1.73 \times 10^8\;m/s$