The velocity of light in a medium is $1.5\times {10}^{8}m/s$. What is the refractive index of the medium with respect to air, if the velocity in air is $3\times {10}^{8}m/s$?

The correct option is B 2
Given : Velocity of medium $=1.5\times {10}^{8}m/sec$.
Velocity of light, $c=3\times {10}^{8}m/sec$.
To find : $n=$?
$n=\frac{c}{v}$
$n=\frac{3\times {10}^8}{1.5\times {10}^8}$
$=2$
$n=2$
Hence, the refractive index of the medium with respect to air is $2$.