Answer:
Option B. Photo-Electric Effect
Explanation:
Photoelectric effect is based on the phenomena that when light having energy equal to the work function of the material is incident on that material, electrons are ejected from the surface of that material as a result of transfer of energy of photons(discrete EM wave energy packets).
Electrons are ejected only when the frequency of photon is more than the threshold frequency.
This experiment led to the understanding of light as a particle (photon) to explain photoelectric effect.
