15. What is ejected from a metal's surface when light of a sufficient frequency shines on it? A. Protons C. Neutrons B. Electrons D. Photons

The correct answer is B. Electrons. When light of a sufficient frequency shines on a metal's surface, it provides energy to the electrons in the metal. This energy can be enough to overcome the binding energy holding the electrons to the metal atoms, causing them to be ejected from the surface. This phenomenon is known as the photoelectric effect.