Answer:
Green, Blue, Indigo, Violet
Explanation:
According to Einstein's equation of photoelectric effect, the kinetic energy of emitted photoelectron is the difference between the energy of the incident photon and the work function of the metal. The work function of the metal referee to the minimum energy that must be supplied in order to eject an electron from a metal surface. The energy of the incident photon must exceed the work function of the metal.
When we look at the electromagnetic spectrum, only the selected colours have frequency above the threshold frequency as shown by the image attached below.
