Ionisation energy of ${\mathrm{He}}^{+}$ is $19·6 \mathrm{x} {10}^{-18} \mathrm{J} {\mathrm{atom}}^{-1}$. The energy of the first stationary state $(\mathrm{n}=1)$ of ${\mathrm{Li}}^{2+}$ is

The radius of the second Bohr orbit for hydrogen atom is ( Planck's constant, $\mathrm{h} = 6·6262 \mathrm{x} {10}^{-34} \mathrm{Js}$, mass of electron$= 9.1091 \mathrm{x} {10}^{-31} \mathrm{kg}$, charge of electron, $\mathrm{e} = 1·60210 \mathrm{x} {10}^{-1 9} \mathrm{C}$, permittivity of the vacuum, ${\in }_{\mathrm{o}}= 8,854185 \mathrm{x} {10}^{-1 2} {\mathrm{kg}}^{-1} {\mathrm{m}}^{-3} {\mathrm{A}}^2$).