X-ray photons with a wavelength of 0.135 nm. express the energy numerically in kilojoules per mole.

Using E=hν where h is Planck's constant and v is the frequency of the photon. In the question above, the wavelenght is given so we can find the frequency of the photon using c=λν. c is a constant = 3*10^8 so frequency is equal to

(3*10^8) / 0.135*10^-9. Then use ur frequency in the eqn above using h 6.626*10^-34