He+ The total energy of a hydrogen-like ion, having Z protons in its nucleus, is given by: E=−n213.6Z2​eV Here, n= Principal quantum numberFor ground state,n=1∴ Total energy, E=-13.6 Z2eV For hydrogen,Z=1∴ Total energy, E=-13.6 eV For deuterium,z=1: Total energv, E=-13.6 eV For He+ Z=2∴ Total energy, E=-13.6 ×22=−54.4eV For Li++ Z=3∴ Total energy, E=-13.6×32=−122.4eV Hence, the ion having an energy of −54.4eV in its ground state may be He+ .