Concept:The number of photo-electrons ejected per second is controlled by the rate of photon arrival on the metal surface.
Explanation:In photo-emission, one photon can release one photo-electron if its energy is sufficient.
This condition depends on the frequency of the light being greater than the threshold frequency.
However, the actual number of photo-electrons released per second depends on the number of photons striking the metal per second.
This is determined by the intensity of the beam.
If the intensity increases, more photons hit the metal each second, so more photo-electrons are ejected per second.
The frequency changes the kinetic energy of the ejected electrons, not their number.
The work function and threshold frequency are properties of the metal, not factors controlling the emission rate.
Answer:D. intensity of the beam