Ionisation energy of He+ is 19.6×10−18J atom −1.The energy of first stationary state (n=1) of Li2+ is

IE=-E1E1 for He+=-19.6×10-18Jatom-1(E1)He+(E1)Li2+=(ZHe+)2(ZLi2+)2-19.6×10-18(E1)Li2+=49E1(Li2+)=-19.6×9×10-184=-4.41×10-17 Jatom-1