Question: A certain species of ionized atoms produces an emission line spectrum according to the Bohr model, but the number of protons Z in the nucleus is unknown. A group of lines in the spectrum forms a series in which the shortest wavelength is 205.1 nm and the longest wavelength is 468.8 nm.
Q- Find the next-to-the-longest wavelength in the series of lines.
I need help for the above question.