Which of the following coloured light has the least speed in glass prism?(a) violet (b) yellow (c) red (d) green

In the spectrum of white light, Red light has the longest wavelength and the least frequency (least deviation), which means it has a maximum speed, whereas, violet light has the shortest wavelength and the highest frequency (maximum deviation), which means it has the minimum speed among all the colours in the visible spectrum.

Therefore, among the given colour of light, violet would have the least speed in a glass prism.