The particle nature of light is demonstrated by the
Answer Details
The sentence "The particle nature of light is demonstrated by the photoelectric effect" means that light can behave as particles, which is demonstrated by the photoelectric effect. The photoelectric effect is a phenomenon where electrons are emitted from a material when light is shone on it, and this can only be explained by treating light as particles, or photons. Therefore, the correct answer is "photoelectric effect". Options (b) "speed of light", (c) "colours of light", and (d) "diffraction of light" are not directly related to the particle nature of light.