Unpolarized light incident on a plane glass surface. What should be the angle of incidence so that the reflected and refracted and refracted ray are perpendicular to each other ? $(\mu =1.5)$

Question

$\begin{array}{1 1} 50^{\circ} \\ 55^{\circ} \\ 56.3^{\circ} \\ 55.3^{\circ} \end{array}$