Answer
Since photons of red light have less energy than photons of yellow light, electrons should not be ejected if red light is used.
An increase in the intensity of yellow light should not cause electrons to be ejected, since an increase in intensity means that more photons are used, but the energy of each individual photon does not change.
Violet light, even very faint violet light, should cause electrons to be ejected since photons of violet light have more energy than photons of green light.
Work Step by Step
In a photoelectric effect experiment, electrons can be ejected as long as the energy of the individual photons are at least as great as the work function of the metal.
Since photons of red light have less energy than photons of yellow light, electrons should not be ejected if red light is used.
An increase in the intensity of yellow light should not cause electrons to be ejected, since an increase in intensity means that more photons are used, but the energy of each individual photon does not change.
Violet light, even very faint violet light, should cause electrons to be ejected since photons of violet light have more energy than photons of green light.
