Q:  Compute the energy of the n=1 state for an iron K-shell electron.

                                                1 
              E(1)  =  (-13.6 eV) * (25^2) *  -----  =  -8500 eV
                                                1

  Q:  Compute the energy of the n=2 state for an iron K-shell electron.

                                                1 
              E(2)  =  (-13.6 eV) * (25^2) *  -----  =  -2125 eV
                                                4


  Q:  If a K-shell electron drops from n=2 to n=1, what is the energy
          of the emitted photon?


             E  =  E(2) - E(1)  =  6375 eV  =  6.4 keV