The energy of hydrogen ion is given byEn​=−n2(13.6eV)Z2​ For the first excited state (n=2), the energy of He+ion (with Z=2 ) will be −13.6eV. This is same as the ground state energy of a hydrogen atom.Similarly, for all the hydrogen like ions, the energy of the (n−1)th excited state will be same as the ground state energy of a hydrogen atom if Z=n.