Question

If the critical angle for total internal reflection from a medium to vacuum is 45°, then velocity of light in the medium is :

(1) 3 × 10⁸ m/s 

(2) 1.5 × 10⁸ m/s

(3) $3\over\sqrt2$ × 10⁸ m/s

(4) $\sqrt2$ × 10⁸ m/s