For a transparent medium relative permeability and permittivity μ_...

The speed of any electromagnetic wave (EM) like light in any medium of permeability, $\mu$ and permittivity, $\varepsilon$ is given by $$\mathrm{v}=\frac{1}{\sqrt{\mu \varepsilon}}$$ Also, $\mu=\mu_0 \mu_r$ and $\varepsilon=\varepsilon_0 \varepsilon_r$ where, $\mu_0$ and $\varepsilon_0$ are permeability and permittivity in free space and $\mu_{\mathrm{r}}$ and $\varepsilon_{\mathrm{r}}$ are relative permeability and relative permittivity of medium respectively. Here, $\mu_{\mathrm{r}}=1.0$ $$\varepsilon_{\mathrm{r}}=1.44$$\begin{aligned} \therefore \quad \quad \quad \mathrm{v} & =\frac{1}{\sqrt{\mu_{\mathrm{r}} \varepsilon_{\mathrm{r}} \mu_0 \varepsilon_0}}=\frac{\mathrm{c}}{\sqrt{\mu_{\mathrm{r}} \varepsilon_{\mathrm{r}}}} \quad\left[\because \mathrm{c}=\frac{1}{\sqrt{\mu_0 \varepsilon_0}}\right] \\ & =\frac{3 \times 10^8}{\sqrt{1 \times 1.44}} \\ & =2.5 \times 10^8 \mathrm{~ms}^{-1} \end{aligned}