As red light shines on a piece of metal, no electrons are released. when the red light is slowly changed to shorter-wavelength light (basically progressing through the rainbow), nothing happens until yellow light shines on the metal, at which point electrons are released from the metal.
if this metal is replaced with a metal having a higher work function, which light would have the best chance of releasing electrons from the metal?

red.
blue.
yellow would still work fine.
we need to know more about the metals involved.

If this metal is replaced with a metal having a higher work function, yellow light may be able to remove electrons but the electrons ejected will have less kinetic energy and the required stopping potential would be less. So in order to remove electrons( with more kinetic energy), we need to use light having even more shorter wavelength than yellow light because light with shorter wavelength possesses more energy and the electrons will eject with greater kinetic energy. Hence BLUE light should be used for better results cuz its wavelength is less than yellow light. Hope it helps.

Blue.

Their frequency red has les frequency, therefore red photons have low energy blue has high frequency ergo. Blue photons have lots of energy, the metal didn't shoot electrons until you shun yellow light, that means, the minimum energy required (the work function) for that metal, was that of the energy of yellow photon