Unpolarised light is incident from air on a plane surface of a material of refractive index '$\mu$ '. At a particular angle of incidence '$i$ ', it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options is correct for this situation?

1. A
   $i={\sin }^{-1}\left(\frac{1}{\mu }\right)$
2. B
   Reflected light is polarised with its electric vector perpendicular to the plane of incidence
3. C
   Reflected light is polarised with its electric vector parallel to the plane of incidence
4. D
   $i={\tan }^{-1}\left(\frac{1}{\mu }\right)$