Electrons each having the energy 80 ke V are incident on the tungsten target of an X-ray tube. The K-shell electrons of tungsten have $-$ 72.5 keV energy. Then, which amongst the following X-ray spectrum is emitted by the tube?

As the energy of the incident electrons is greater than the magnitude of the energy of the K -shell electrons, the target atoms will have vacancies in the K-shell (K-shell electrons will be knocked out). This will cause emission of the entire characteristic spectrum of tungsten. Along with this, continuous X-rays will always be present, with

${\lambda }_c=\frac{1242 \mathrm{nm}-\mathrm{eV}}{80\times {10}^3\mathrm{eV}}\cong 0.0155 \mathrm{nm}$