The refractive index of a material depends on the wavelength of the incident light; this phenomenon is known as dispersion. Light with shorter wavelengths is refracted more than light with longer wavelengths. Among visible light, violet has the shortest wavelength (about 380–450 nm), while red has the longest (about 620–750 nm).
When white light passes through glass, violet light bends the most due to its higher refractive index, resulting in maximum deviation. This explains why the refractive index of glass is maximum for violet color. Conversely, red light bends the least, having the lowest refractive index in glass.
This wavelength-dependent refractive behavior is the principle behind the formation of rainbows and the splitting of light by a prism.
Among the given colors, violet light has the shortest wavelength, and hence, the refractive index is maximum for violet light.