Which of the following phenomena can explain the quantum nature of light?

In the photoelectric effect, keeping the frequency of incident radiation and the accelerating potential fixed, if the intensity of incident light is increased,

Two metallic plates $A$ and $B$,each of area $5 \times 10^{-4} \, m^2$,are placed parallel to each other at a separation of $1 \, cm$. Plate $B$ carries a positive charge of $33.7 \, pC$. $A$ monochromatic beam of light,with photons of energy $5 \, eV$ each,starts falling on plate $A$ at $t = 0$,so that $10^{16}$ photons fall on it per square meter per second. Assume that one photoelectron is emitted for every $10^6$ incident photons. Also assume that all the emitted photoelectrons are collected by plate $B$ and the work function of plate $A$ remains constant at $2 \, eV$. The electric field between the plates at the end of $10 \, seconds$ is:

Assertion : The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.
Reason : The work function of the metal varies as a function of depth from the surface.

One milliwatt of light of wavelength $4560 \ \mathring{A}$ is incident on a cesium surface of work function $1.9 \ eV$. Given that the quantum efficiency of photoelectric emission is $0.5\%$. Planck's constant $h = 6.62 \times 10^{-34} \ J \cdot s$,velocity of light $c = 3 \times 10^8 \ m/s$,the corresponding photoelectric current is:

Why is photoelectric current proportional to intensity?