Explanation

The stopping potential is the voltage applied to the electrodes in a photoelectric effect experiment that just prevents the most energetic electrons from reaching the anode.

Since the kinetic energy of the ejected electrons is directly proportional to the frequency of the incident light (above the threshold frequency), a higher frequency light will result in more energetic electrons.

Therefore, the stopping potential, which is the voltage needed to completely stop these most energetic electrons, is also directly proportional to their energy.