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

Threshold frequency for a metal is $10^{15} \ Hz$. Light of $\lambda = 4000 \ \mathring{A}$ falls on its surface. Which of the following statements is correct?

Show that wave theory cannot explain fundamental characteristics of photoelectric effect.

Light of frequency $1.5$ times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled?

$A$ caesium photocell,with a steady potential difference of $60 \ V$ across it,is illuminated by a bright point source of light $50 \ cm$ away. When the same light source is placed $1 \ m$ away,the photoelectrons emitted from the cell:

When monochromatic radiation of intensity $I$ falls on a metal surface, the number of photoelectrons and their maximum kinetic energy are $N$ and $K$ respectively. If the intensity of radiation is $2I$, the number of emitted electrons and their maximum kinetic energy are respectively