Concept: The photoelectric effect provides evidence that light behaves as particles (photons).Explanation:• The photoelectric effect occurs when light shining on a metal surface causes electrons to be emitted.• This effect can only be explained if light consists of discrete packets of energy called photons, each with energy E=hf.• Wave theory alone cannot explain why electron emission depends on frequency rather than intensity.• Therefore, the particle nature of light is demonstrated by the photoelectric effect.Answer: A. photoelectric effect