What is the charge on $\gamma$-rays?

Find the wavelength of radiation having frequency $4 \times 10^{11} \ kHz$.

If light waves pass through a $Nicol$ prism,then all the oscillations occur only in one plane. Such a beam of light is called:

The frequency of a radio wave from Mars to Earth is $6 \times 10^3 \, s^{-1}$. If the distance between them is $8 \times 10^7 \, km$,how much time will it take?

The photoelectric effect can be caused by which of the following?

Which of the following statements is correct about the photoelectric effect?
$1$. The number of electrons ejected from a metal surface is inversely proportional to the intensity of light.
$2$. Below the threshold frequency,the photoelectric effect can be observed.
$3$. At a frequency higher than the threshold frequency,the ejected electrons have a certain kinetic energy.
$4$. At a frequency higher than the threshold frequency,the electron is still on the metal surface.