An l-shell electron (binding energy = 26 kev) is removed from an atom that has an m-shell binding energy of 4 kev and an n-shell binding energy of 1 kev. if a free electron fills the vacancy in the l-shell, the characteristic x-ray produced will have an energy of

26 keV

Explanation:

The electron is being ejected from the L -shell which has a binding energy of 26 keV.

Now the electron is being added to fill the vacancy in the L shell. Since, the binding the energy of the electron for the L-shell is 26 keV, so the energy produced is also equal to this amount of energy.

So, the characteristic x-ray produced will have an energy of 26 keV.