To solve this problem, we need to determine the velocity of light $v$ in a material medium with given relative permittivity $\varepsilon_r$ and relative permeability $\mu_r. \\$The velocity of light in a medium is given by the formula:$\\ v = \frac{c}{\sqrt{\varepsilon_r \mu_r}} \\$where:$\\$• $c$ is the velocity of light in vacuum.$\\$• $\varepsilon_r$ is the relative permittivity of the medium.$\\$• $\mu_r$ is the relative permeability of the medium.$\\$Let's analyze the options provided:$\\$Option 1: $v = c \\$Option 2: $v = \frac{c}{\sqrt{\mu_r \varepsilon_r}} \\$Option 3: $v = \sqrt{\frac{\mu_r}{\varepsilon_r}} \\$Option 4: $v = \frac{c}{\mu_r \varepsilon_r} \\$The correct formula for the velocity of light in a medium is $v = \frac{c}{\sqrt{\varepsilon_r \mu_r}}. \\$This matches Option 2.$\\$Therefore, the correct answer is Option 2: $v = \frac{c}{\sqrt{\mu_r \varepsilon_r}}.$