$\left[{h}=4.14 \times 10^{-15} \,{eVs}, {c}=3 \times 10^{8}\, {ms}^{-1}\right]$
\({E}_{k_{a}}=E_{k}-E_{L}\)
\(\frac{h c}{\lambda_{k_{a}}}=E_{k}-E_{L}\)
\(E_{L}= E_{k}-\frac{h c}{\lambda_{k_{a}}}\)
\(=27.5 {KeV}-\frac{12.42 \times 10^{-7}\, {eV\,m}}{0.071 \times 10^{-9}\, {m}}\)
\(E_{L}=(27.5-17.5)\, {keV}\)
\(=10\,{keV}\)