The speed of light in a medium is inversely proportional to the refractive index of that medium. A vacuum has the lowest refractive index (n=1), hence the highest speed of light.
The velocity of light is the highest in (1) Water (2) Air (3) Vacuum (4) Glass
Asked in School Lecturer 2015 · Topic: Optics (Reflection and Refraction at plane and spherical surfaces)
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