Question

will a spectrum be formed if blue light fall on a prism ? give reason ?

Answer 1

White light is a combination of 7 colors, so it can form a spectrum. Blue light is not a combination of seven colors and thus it will not form a spectrum when it will fell on the prism. 

Answer 2

No, spectrum will not form when blue light falls on a prism because seven colours are made up of white light . And this white light disperses into seven colours.