A ray of light selling in a transparent medium of refractive index $\mu$, falls on a surface separating the medium from the air at an angle of incidence of $45^0$. For which of the following values of $\mu$ the ray can undergo total internal reflection?

A ray of light incident parallel to the base PQ of an isosceles right-angled triangular prism PQR suffers two successive total internal reflections at the faces PQ and QR before reversed in direction as shown.  If the refractive index of the material of the prism is $\mu$, then find the value of $\mu$.