Refractive index is the ratio of  speed of light in two media. refractive index of medium 1 with respect to medium 2 is   speed of light in medium 2 ÷ speed of light in medium 1.m2/m1
1 2 1
The ratio of the velocity of light V1 in medium 12 the velocity V2 in medium to is known as relative refractive index of medium to with respect to the medium one it is denoted by n21
N 2 1 is equal to v 1 divided by v 2

the refractive index of medium with respect to the vacuum is called the absolute refractive index of that medium
Bharti Nagar Chanda the ratio of the velocity of light in vacuum to velocity of light in medium is known as absolute refractive index n is equal to c upon v

Absolute refractive index of any medium is always greater than 1. hope this helps plz mark as brainliest