Question

what means lowest refractive index

Answer 1

refractive index is also called index of refractiin.when a light ray is transferd through one medium to another called refractive index.
example: air have lighter refractive tahn water.

Answer 2

Definition of refractive index 

: the ratio of the speed of radiation (such as light) in one medium (such as air, glass, or a vacuum) to that in another medium

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