Predict why the refractive index of air is slightly higher than the refractive index of...

The refractive index of a medium is defined as $n=\frac{c}{v}$, where c is the speed of light in a vacuum and v is the apparent velocity of light traveling through that medium.
The refractive index of a vacuum is $\frac{c}{c}=1$.
Since light seems to travel slower in air (but not by much since air is not as optically dense), the refractive index will be greater $\frac{c}{v}>1$ since 0