The speed of light in a medium depends on :

The correct answer is Option (3) → wavelength

The speed of light in a medium is \( v = c/n \), where \( n \) is the refractive index of the medium. The refractive index of a material is different for different colours: this is dispersion. So \( v \) depends on the medium and on the wavelength of the light.

NCERT (2026-27):
Refraction – “… We note that n₂₁ is a characteristic of the pair of media (and also depends on the wavelength of light), but is independent of the angle of incidence.”