Which of the following shows the particle nature of light?

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

On a photosensitive surface, if the intensity of incident radiation is increased, the stopping potential

Light of wavelength $4000 Å$ is incident on a sodium surface for which the threshold wavelength of photoelectrons is $5420 Å$. The work function of sodium is (in $eV$)

When the distance of a light source from a photocell is $r_1$,the photoelectric current is $I_1$. If the distance is $r_2$,the photoelectric current becomes $I_2$. The ratio $(I_1 : I_2)$ is .....

$A$ point source causes the photoelectric effect from a small metal plate. Which of the following curves may represent the saturation photocurrent $(I)$ as a function of the distance $(r)$ between the source and the metal?