The Figure Shows the Energy-Level Diagram of an X-Ray Machine $\alpha$

The figure shows the energy-level diagram of an X-ray machine with a nickel target that is being operated at a potential of 50 keV. The photon wavelength of the allowed K _$\alpha$ emission X rays is approximately

A) 0.165 nm
B) 0.176 nm
C) 0.501 nm
D) 0.149 nm
E) 0.994 nm