In photo-emission, the number of photo-electrons ejected per second depends on the

The question is asking about the factor(s) that determine the number of photo-electrons ejected per second in photo-emission. In photo-emission, electrons are emitted from a metal surface when light is shone on it. The energy of the photons in the light must be greater than the work function of the metal for this to occur. So, the answer to the question is that the number of photo-electrons ejected per second depends on the work function of the metal. The other options given are also related to photo-emission, but do not directly affect the number of photo-electrons ejected per second. The frequency of the beam and the threshold frequency of the metal are related to the minimum energy required for photo-emission to occur, while the intensity of the beam affects the number of photons hitting the metal surface, but not the number of electrons ejected per second.