For the same angle of incidence in media $P, Q$ and $R$,the angles of refraction are $45^{\circ}, 35^{\circ}$ and $15^{\circ}$ respectively. In which medium will the velocity of light be minimum? Give reason.

(C) We know that the refractive index $n$ is given by $n = \frac{\sin i}{\sin r}$.
For a constant angle of incidence $i$,the refractive index $n$ is inversely proportional to $\sin r$.
Since the angle of refraction $r$ is minimum for medium $R$ $(15^{\circ})$,the refractive index $n$ is maximum for medium $R$.
We also know that the velocity of light $v$ in a medium is given by $v = \frac{c}{n}$,where $c$ is the speed of light in a vacuum.
Since $v$ is inversely proportional to $n$,the velocity of light will be minimum where the refractive index $n$ is maximum.
Therefore,the velocity of light is minimum in medium $R$.