Question

A perfectly monochromatic light source
is not possible. Explain on the basis of
Heisenberg uncertainty principle.​

Answer 1

One can come up with a very narrow-banded light source, but it is impossible to have a truly monochromatic light because of the the Heisenberg's uncertainty principle (HUP), even though the HUP does not impose a certainty limit to each observable. ... Monochromatic light is a wave with exactly one frequency.