Refractive index of the medium having absolute permeability $\mu$ and absolute permeability $\epsilon$ is

$\mu_0 - \text{Permeability of free space}$

$\epsilon_0 -  \text{Permitivitty of free space}$

$\mu_r - \text{Relative Permeability}$

$\epsilon_r - \text{relative Permitivitty}$

$\sqrt{\mu_r \epsilon_r}$

$\text{Speed of light in vacuum is c }= \frac{1}{\sqrt{\mu_0 \epsilon_0}}$

$\text{Speed of light in a mdium is v }= \frac{1}{\sqrt{\mu \epsilon}}$

$ \text{Refractive index } = \frac{c}{v} = \sqrt{\mu_r \epsilon_r}$