Question

What is SI unit of Refracrive index ?​

Answer 1

Refractive Index has no units as it is just a ratio.

^-^

Answer 2

See,

Refractive index means ratio of speed of light in given pair of media.

Since, on both numerator and denominator there is speed it means unit on both sides are same, so they cancel out each other.

Thus, Refractive index has no unit.