Violet colour in the spectrum is at the bottom whereas red colour is at the top why

The difference is due to the difference in their wavelength. red has the longest wavelength whereas blue has the shortest wavelength. as white light enters the prism and deviates from its original path into component colors, this deviation is caused by different refractive indices of each of the component wavelengths of light. those that have shorter wavelength will disperse or deviate more than those that have longer wavelength. thus, red light having longest wavelength, deviates the least and is at the top whereas blue light, having the shortest wavelength, deviates the most and is at the bottom