Question

What is refractive index?

Answer 1

refractive index is the ratio of speed of radiation in one medium (such as air, glass )to that in another medium

Answer 2

Refractive index is the amount of refraction from a rarer medium to a denser medium.

Refractive index = sin i/ sin r

Where,

i = angle of incidence

r = angle of refraction

It is a ratio and does not have a unit.

Hope it helps.