A ray of light is incident on a glass plate at an angle of ${60}^{\circ }.$ What is the refractive index of glass if the reflected and refracted rays are perpendicular to each other?

• A

  $\tan {60}^{\circ }$

• B

  $\cot {60}^{\circ }$

• C

  $\sin {60}^{\circ }$

• D

  $\cos {60}^{\circ }$