\(E=\frac{h c}{\lambda}\)

\( \Rightarrow \quad 2.5{\rm{eV}} = \frac{{{\rm{hc}}}}{{5000 \times {{10}^{ - 10}}}}\)  (as \(\lambda  = 5000\) \(\mathop {\rm{A}}\limits^o \))

\(\Rightarrow \mathrm{hc}=2.5 \times 5 \times 10^{-7} \mathrm{\,eV}\)

For \(\mathrm{X}-\) ray photon, \(\mathrm{c}=\) same, \(\mathrm{h}=\) constant

\(\Rightarrow \mathrm{E}=\frac{\mathrm{hc}}{\lambda_{\mathrm{x}-\mathrm{ray}}}\)

\(=\frac{2.5 \times 5 \times 10^{-7}}{1 \times 10^{-10}} \mathrm{eV}\)

\(=2.5 \times 5000 \mathrm{\,eV}\)