A point source causes photoelectric effect from a small metal plate. Which of the following curves may represent the saturation photocurrent as a function of the distance between the source and the metal ?

Saturation current is the maximum current possible and it will be directly proportional to the number of electrons falling on collector plate per second which depends on number of photons incident on the cathode as one photon contribute in one electron and the number of photons is actually proportional to intensity which varies as : Intensity I∝1r2 ​ , Where r is the distance between source and metal plate.