What is the relation between the polarising angle and refractive index?

Hint:Brewster was capable of determining that the medium's refractive index is numerically equal to the tangent angle of polarization. Brewster's law gives the relationship of light waves at the highest polarization angle of light.

Complete step-by-step solution:
Brewster’s law provides the relation between the polarising angle and the refractive index. It is examined experimentally that when the light falls at the polarising angle, the refracted ray and the reflected ray are perpendicular to each other. According to this law, the tangent of the angle of polarization is equal to the medium's refractive index.
Brewster law gives,
$\mu = \tan \theta_{p}$
$\mu$ is the refractive index.
$\theta_{p}$ is a polarising angle.
Brewster's angle (also appreciated as the polarization angle) is an incident angle at which light with a unique polarization is ideally passed through a transparent dielectric surface with no glare. When unpolarized light falls at this angle, the light reflected from the outside is therefore perfectly polarized.

Note:Brewster’s law gives a relationship for light waves stating that the maximum polarization of a ray of light may be obtained by letting the beam fall on an outside of a transparent medium in such a system that the refracted ray creates an angle of $90^{\circ}$ with the reflected beam.