A ray of light is incident on side of a right angled prism normally. It then falls on the hypotenuse of the prism and gets reflected back as shown. If $\theta=45^{\circ}$ then the refractive index of the material of prism is

Question

$(a)\;1 \\ (b)\;< \sqrt 2 \\ (c)\;=\sqrt 2 \\ (d)\; > \sqrt 2 $