When the angle of incidence on a material is 60°, the reflected light is completely polarised. The velocity of the refracted ray inside the material in cm/s is:

$\sqrt{3} \times 10^8$

The correct answer is Option (3) → $\sqrt{3} \times 10^8$

According to Brewster's law,

$μ=\tan(θ_B)$ [μ = Refractive index]

$⇒μ=\tan(60°)=\sqrt{3}$

and,

$v=\frac{c}{μ}$ [v = velocity of light in a material]

$v=\frac{3×10^8}{\sqrt{3}}=\sqrt{3} \times 10^8m/s$