A ray of light from a rarer medium strikes a denser medium as shown in the figure . The reflected and refracted rays make an angle of $90^{\circ}$ with each other . The angles of reflection and refraction are r and r' , the critical angle would be

Question

$\begin{array}{1 1} \sin ^{-1} (\tan r) \\ \tan ^{-1} (\sin r ) \\ \sin ^{-1} (\tan n r') \\ \tan ^{-1} (\sin r') \end{array}$