(b) A regular series of lines observed in the visible part of the emission spectrum of a cosmic star has the property that one of its emission lines coincides with the first line of the hydrogen Balmer series, and that every 5th, 10th, 15th, etc. line afterwards coincides with 2nd, 3rd 4th etc. line of the hydrogen Balmer series. Assuming that this particular series in the emission spectrum of the star can be associated with a hydrogen-like ion, what element would be responsible for the observed emission? What is the longest wavelength that can be found in this particular spectral series? Hint: the atomic number should give you a clue about the element in question.​