For the same angle of incidence, the angles of refraction in three different media P, Q and R are $45°,35°$ and $15°$respectively. In which medium, will the speed of light be minimum?

The speed of light is minimum in R medium.
Assume that the medium has a refractive index of$\mathrm{ n}$ and that air has a light speed of$\mathrm{ c}$.
Using the refraction law of Snell:
 Where$\mathrm{ }{\mathrm{n}}_{\left(\mathrm{air}\right)}\mathrm{ }=\mathrm{ }1$
    $1\times \sin \left(\mathrm{i}\right)\mathrm{ }=\mathrm{n}\times \sin (\mathrm{r}$)
$\Rightarrow \mathrm{ n}=\frac{\sin \left(\mathrm{i}\right)}{\sin \left(\mathrm{r}\right)}$
The velocity of light in a medium, $\mathrm{V}=\frac{\mathrm{c}}{\mathrm{n}}$
                                                     $=\frac{\mathrm{c}\times \sin \left(\mathrm{r}\right)}{\sin \left(\mathrm{i}\right)}$
$\Rightarrow \mathrm{v }\propto \mathrm{ sin}\left(\mathrm{r}\right)$
Thus, Since R has the least angle of refraction, medium R has the lowest light velocity.