Final answer:
To increase the number of electrons ejected per second from a metallic surface, the intensity of the light must be increased, which raises the number of photons and hence the chance of electron emissions.
Step-by-step explanation:
When a metal surface is exposed to blue light, electrons are emitted through the photoelectric effect. To increase the number of electrons ejected per second, one can increase the intensity of the light. This action increases the number of photons hitting the surface, which in turn increases the probability of electron emissions without affecting their kinetic energy. However, if the frequency of the incoming light is below the metal's threshold frequency, increasing intensity alone will not result in electron ejection. Once the frequency is above the threshold, any increase in intensity will raise the count of ejected electrons.