Question

define optical denser medium

Answer 1

when Light bent or goes one medium to another medium
then there is a decrease in speed of light
the medium in which the speed of light decreases is called optical denser medium!!

Answer 2

A medium ‘A’ is said to be optically denser then medium ‘B’, if the speed of light in ‘A’ is lesser than the speed of light in ‘B’ i.e the refractive index of ‘A’ is greater than the refractive index of ‘B’.