The path of a light ray, from air to three different media A, B and C for a given angle of incidence. Study the diagram, carefully and answer the following questions.

The optically rarer medium is

C is the optically rarer medium.
Optically rarer medium is the medium in which the speed of light is more. For example, the air is an optically rarer medium than glass and water.
We know that refractive angle and refractive index are inversely proportional to each other. The optical density is directly proportional to the refractive index of the medium. The optically denser medium is A, as the refractive index is less.