Final answer:
The photoelectric effect suggests that electromagnetic radiation behaves like a particle, as it involves electrons being ejected from a metal due to the absorption of photons with sufficient energy. This behavior cannot be explained by wave theory alone and directly aligns with the particle nature of light. Aspects such as the ejection of electrons after a threshold frequency and the energy of these electrons support the particle theory.
Step-by-step explanation:
Among the phenomena listed, the one that suggests that electromagnetic radiation is a particle is the photoelectric effect. This phenomenon is best explained by the particle nature of light as described by the concept of photons. In the photoelectric effect, electrons are ejected from a metal when it is exposed to light of sufficiently high frequency, regardless of the intensity of the light. This behavior cannot be explained using a wave description of light, where increasing the light intensity should eject electrons, even if the frequency is low, which is not observed in practice.
The photoelectric effect is a direct consequence of the particle character of electromagnetic radiation. Visible light is not the only type of electromagnetic radiation that can cause the photoelectric effect; any electromagnetic radiation with a frequency above the threshold frequency specific to the material can cause this effect. This further supports the particle description of light, as it is the energy of the photons, not the overall wave intensity, that determines the ability to cause the photoelectric effect.