The momentum of a photon in an $X-$ray beam of $10^{-10} \ m$ wavelength is

$A$ scientist claims to have a perfect technique in which he can spontaneously convert an electron completely into energy in the laboratory without any other material required. What is the conclusion about this claim from our current understanding of physics?

$A$ particle which has zero rest mass and non-zero energy and momentum must travel with a speed

Which one of these is non-divisible?

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

Consider two black bodies $A$ and $B$ having equal surface areas. On the surface of $A$, $n$ photons of frequency $f$ are incident perpendicularly in a time $t$. On the surface of $B$, $2n$ photons of frequency $3f$ are incident perpendicularly in a time $4t$. The ratio of average intensity of radiation on surface $A$ to that on surface $B$ is