Which phenomena can be explained by using the particle nature of light?

Photoelectric effect is produced by a point source on a small metal plate. Which of the following curves represents the saturation photoelectric current as a function of the distance between the source and the metal?

$A$ photoelectric cell is illuminated by a point source of light placed at a distance of $1 \ m$. If the source is moved to a distance of $2 \ m$,then:

In a photoelectric experiment,a parallel beam of monochromatic light with power of $200 \ W$ is incident on a perfectly absorbing cathode of work function $6.25 \ eV$. The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is $100 \%$. $A$ potential difference of $500 \ V$ is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force $F = n \times 10^{-4} \ N$ due to the impact of the electrons. The value of $n$ is. . . . .
Mass of the electron $m_e = 9 \times 10^{-31} \ kg$ and $1.0 \ eV = 1.6 \times 10^{-19} \ J$.

Define threshold frequency and on which factor does threshold frequency depend?

The wave picture of light has failed to explain which of the following phenomena?