The ability of a medium to change the path of light
 I'm sorry I don't know whether my answer is correct.if it is please mark it as the brainliest or rate my answer
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The Brainliest Answer!
It is the density of the object which depends when the path of the light enters it and bends towards the direction of the normal. if the path of the light bending towards the normal is more than this medium is called denser medium and if it is less it is called rarer medium
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