For hydrogen and hydrogen like atoms En=−13.6(n2)(Z2)eV
Therefore, ground state energy of doubly ionized lithium
atom (Z = 3, n = 1) will be E1(−13.6)(1)2(3)2=−122.4eV ∴ Ionization energy of an electron in ground state of doubly ionized lithium atom will be 122.4 eV.