Question

1. What is refractive index? Which medium has
the lowest value of refractive index ?​

Answer 1

Answer:

Refractive Index (Index of Refraction) is a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density. The refractive index variable is most commonly symbolized by the letter n or n' in descriptive text and mathematical equations.

Answer 2

Answer:

The refractive index is the measure of bending of a light ray when it passes  from one medium to another. It can be also defined as the ratio of the speed of light in vacuum to that in another medium.

Air has the lowest value of refractive index.