The xz plane is the boundary between two transparent medium. Medium-I with $y\ge 0$ has refractive index $\mu$ and medium –II with $y\le 0$ has a refractive index 1. A ray of light in  medium-I, given by vector $\overrightarrow{n}=\widehat{i}-\sqrt{3}\widehat{j}$ is incident on the plane of separation. If the  reflected and refracted rays make an angle of ${90}^o$ with each other, then the value of $\mu$ is $\sqrt{k}.$ Find the value of k.