Question

the refractive index of diamond
is 2.42 what is meaning of this statement​

Answer 1

by saying the refractive index of diamond is 2.42 we we mean that the ratio of the speed of light in air to the speed of light in glass is equal to 2.42

Answer 2

When we say refractive index of diamond is 2.42, it means light is travelling from rarer to denser medium, and speed of light in air (vacuum) is2.42 times the speed of light indiamond.