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An unpolarized light beam travelling in air is incident on a medium of refractive index $1.73$ at Brewster's angle. Then-
Explanation
At Brewster's angle, $\tan\theta_B = \mu = 1.73 \approx \sqrt{3} \implies \theta_B \approx 60^\circ$. Reflected light is completely plane-polarized with angle of reflection equal to $60^\circ$.
Detailed Solution
According to Brewster's law, when light is incident at Brewster's polarizing angle $\theta_B$: $\tan\theta_B = \mu = 1.73 \approx \sqrt{3} \implies \theta_B = 60^\circ$. By the law of reflection, the angle of reflection is equal to the angle of incidence, i.e., $60^\circ$. At this angle, the reflected light is completely linearly polarized with vibrations perpendicular to the plane of incidence, whereas the transmitted/refracted beam is only partially polarized.