I. The shadow cast by a small bead placed in laser light has a bright spot in the middle II. Adjusting the intensity of the light incident on a piece of metal has no effect on the energy of the photoelectrons produced III. Electrons confined to a region of space can exist only in discrete energy levels 13. Which row below gives the model required to explain each of the observations above?

I. The shadow cast by a small bead placed in laser light has a bright spot in the middle II. Adjusting the intensity of the light incident on a piece of metal has no effect on the energy of the photoelectrons produced III. Electrons confined to a region of space can exist only in discrete energy levels 13. Which row below gives the model required to explain each of the observations above?