[b]The frequency of light in air does not change.[/b]
It is the ratio of the speed of light in air compared to the speed of light in a given substance:
Refractive index of a substance = (speed of light in a vacuum) [divide] (speed of light in substance)
The refractive index of light in air is [b]1.000293[/b] (but 1 is accepted), whereas in water it is [b]1.33... recurring[/b].
The [b]wavelength[/b] of a substance also changes, when refracted, so they are also relative to the refractive index in one way or another.
Therefore the following equations are all true:
[img style='width:100vw' src='https://res.cloudinary.com/deylrqt2d/image/upload/v1487969651/refractive_index_equations_x6mgaw.svg']