What is the charge on a photon?

$A$ photon of frequency $v$ has a momentum associated with it. If the speed of light is $c$,then the momentum is .......

If the energy of a photon corresponding to a wavelength of $6000 \mathring A$ is $3.32 \times 10^{-19} \ J$,the photon energy for a wavelength of $4000 \mathring A$ will be ............ $eV$.

What is the energy of a photon whose wavelength is $6840\,\mathring{A}$? (in $eV$)

Which of the following phenomena cannot be explained by the wave theory of light?

Two sources of light emit $X$-rays of wavelength $1 \ nm$ and visible light of wavelength $500 \ nm$,respectively. Both sources emit light of the same power $200 \ W$. The ratio of the number of photons emitted per second by the $X$-ray source to the number of photons emitted per second by the visible light source is: