b
lonisation energy \((IE) -\) It is the energy required to move an electron from ground state to infinity.

\(\mathrm{IE}=E_{\infty}-E_{1}=0-E_{1}=-E_{1}\)

\(\therefore \mathrm{E}_{1}\) of \(\mathrm{He}^{+}=-19.6 \times 10^{-18} \) \(\mathrm{J}\; atom ^{-1}\)

Energy of a species at \(n\) state,

\(\left(\mathrm{E}_{\mathrm{n}}\right)_{species}\)\(=\left(\mathrm{E}_{\mathrm{n}}\right)_{\mathrm{hydrogen }} \times \mathrm{z}^{2}\)

\(\therefore\left(\mathrm{E}_{1}\right)_{\text {hydrogen }}=\frac{-19.6 \times 10^{-18}}{4}\)\([\text { For } \mathrm{He}, \mathrm{Z}=2]\)

\(\left(E_{1}\right)_{L^{*}}=\frac{-19.6 \times 10^{-18}}{4} \times 3^{2}\)

\(=-4.41 \times 10^{-17} \mathrm{J}\) \(atom\) \(^{-1}\)