calculate the wavelength of light required to ionize a sodium ion?

Question

Calculate the maximum wavelength, in nm. IE of Na+ is 4560 Kj/mole

Answer 1

Energy required for ionizing a single Na atom=IE/A, where A=Avogadro number=6.022e23 per mol

Energy carried by a single photon of light with frequency f,
E=hf, h=Planck's constant=6.6.26e-34 m2 kg /s

Equating the two we get, f=IE/(A*h) = 1.1428e16 Hz

Using speed=wavelength*frequency,
wavelength=3e8/1.1428e16 =2.625e-8 m

Therefore wavelength of light required is 26.25 nm