The quantum nature of light is supported by the photoelectric...

The photoelectric effect provides evidence for the quantum nature of light (photon theory) by explaining phenomena that classical wave theory could not:

According to the photon theory, light consists of discrete energy packets (photons) with energy $E = h\nu$. The maximum kinetic energy of emitted photoelectrons is given by Einstein's photoelectric equation K_\max = h\nu - \Phi, which shows it depends solely on the frequency $\nu$ and not on the intensity of light.

The emission of photoelectrons is an instantaneous process. A single photon transfers its entire energy to an electron at once, leading to immediate emission even if the light is faintly illuminated. Classical wave theory incorrectly predicts a time delay for energy accumulation.

There exists a minimum threshold frequency $\nu_0 = \dfrac{\Phi}{h}$ below which no emission occurs, regardless of the intensity. Wave theory incorrectly predicts that sufficiently intense light of any frequency should eventually cause emission.

The quantization of electric charge is a fundamental property of matter (electrons), not light, and is not related to the quantum nature of light.