Answer:
in the material to the speed of light in a vacuum
Step-by-step explanation:
When a light ray enters from one medium to another, it bends. This is because the speed of light decreases as it enters a medium having more optical density. The speed of light is maximum in vacuum.
The refractive index determines the optical density of a medium. It is the ratio of the speed of light in the vacuum (c) to the speed of light in the material it is passing through (v).