For alkali metals, threshold frequencies lie in which region?

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 is its characteristic property.

Assertion : Kinetic energy of photoelectrons emitted by a photosensitive surface depends upon the intensity of incident photon.
Reason : The ejection of electrons from a metallic surface is possible with a frequency of incident photon below the threshold frequency.

Light of frequency $1.5 \nu_0$ (where $\nu_0$ is the threshold frequency) is incident on a photosensitive material. If the frequency is halved and the intensity is doubled,what happens to the photocurrent?

Light of wavelength $4000 \ \mathring A$ is incident on a sodium surface,where the threshold wavelength for photoemission is $5420 \ \mathring A$. The work function of sodium is ............ $eV$.

$A$ 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