The dispersion of light takes place due to reasons given as follows:

Variation in Wavelengths: Different colors in white light have different wavelengths. Shorter wavelengths (like blue and violet) slow down more than longer wavelengths (like red) when passing through a medium.

Change in Speed: When light enters a denser medium, each color bends (refracts) by a different amount based on its speed. Shorter wavelengths bend more, causing the separation of colors.

Refractive Index: Each color has a slightly different refractive index in the same medium, which leads to each color traveling at a slightly different angle and speed, spreading out to form a spectrum.

Hence, red light has maximum speed and deviates the least while violet light had minimum speed and deviates the most. The deviations of other colors occupy intermediate positions between the violet and red colors.