Since the relationship is directly proportional between the speed of light and wavelength, then the wavelength must decrease since the prism has a higher index of refraction than the air.

Does wavelength change in prism?

Yes, the wavelength changes when the light enters the prism, but it changes right back when it exits. This is a phenomenon called dispersion of light. White light is a mixture of all colours which get separated when they pass through a prism.

How does prism depend on wavelength?

If the ray of light passes from the surroundings into the prism, then the refractive index of the prism depends on the refractive index of the surrounding medium, the nature of the medium also known as optical density, wavelength of the light and the temperature of the surroundings.