Refractive index of the medium having absolute permeability $\mu$ and absolute permeability $\epsilon$ is
$\mu_0 - \text{Permeability of free space}$
$\epsilon_0 - \text{Permitivitty of free space}$
$\mu_r - \text{Relative Permeability}$
$\epsilon_r - \text{relative Permitivitty}$
Answer & explanation
Correct answer: option 2
$\text{Speed of light in vacuum is c }= \frac{1}{\sqrt{\mu_0 \epsilon_0}}$
$\text{Speed of light in a mdium is v }= \frac{1}{\sqrt{\mu \epsilon}}$
$ \text{Refractive index } = \frac{c}{v} = \sqrt{\mu_r \epsilon_r}$