The quantum nature of light is explained by which of the following phenomena?

The time taken by a photoelectron to come out after the photon strikes is approximately

$A$ photocell is illuminated by a small source of light placed at a distance of $1 \ m$. When the same source of light is placed at a distance of $1/2 \ m$,the number of electrons emitted by the photocathode will .......

$A$ photocell is illuminated by a small bright source placed $d \; m$ away. When the same source of light is placed $\frac{d}{2} \; m$ away,the number of electrons emitted by the photocathode would

$A$ $5\; W$ source emits monochromatic light of wavelength $5000\; Å$. When placed $0.5\; m$ away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of $1.0\; m$, the number of photoelectrons liberated will

Light of frequency two times the threshold frequency is incident on a photosensitive material. If the incident frequency is made $\left(\frac{1}{3}\right)^{rd}$ and intensity is doubled,then the photoelectric current will