For hydrogen and hydrogen-like atoms En=−13.6(n2)(Z2)eV
Therefore, the ground state energy of doubly ionized lithium atom (Z=3,n=1) will be En=−13⋅6(1)2(3)2=−122⋅4eV ∴ The ionization energy of an electron in the ground state of doubly ionized lithium atom will be 122.4 eV