For which colour, the refractive index of glass is maximum?

The correct option is B

violet

Explanation for the correct answer,

1. A refractive index is a property of the material through which the ray is passing through.
2. The index of refraction also depends on the wavelength of the light. The refractive index changes inversely with the wavelength.
3. For the given options, the increasing order of the wavelength of the colors is given as violet, green, yellow, and red.
4. Thus, the violet ray has the shortest wavelength. So, it has the highest refractive index.

Thus, option (b) is correct.