D. no unit
What Is Refraction:
Refraction is the bending of light. It occurs when light moves from one medium to another, causing it to slow down or speed up. The refractive index is a measure of how much refraction or bending of light occurs.
What is the S.I unit of the refractive index?
The refractive index has no units due to the same quantities. These units cancel each other when calculating the value.