Series of spectral lines 1. Lyman series (n′=1) - The series is named after its discoverer Theodore Lyman. - Lyman series lies in the ultraviolet region. 2. Balmer formula(n′=2) - The series is named after its discoverer Johann Balmer. - It is technically visible part of the spectrum with wavelength longer than 400nm and shorter than 700nm. 3. Paschen series(n′=3) - Named after the German physicist- Friedrich Paschen - The paschen lines all lie in the infrared band. 4. Brackett series(n′=4) - Named after the American physicist Frederick Sumner Brackett. - The spectral lines of Brackett series lie infrared band. 5. Pfund series (n′=5) - Discovered by August Herman Pfund. - Lie in infrared region. 6. Humphreys series (n′=6) - American physicist Curtis J. Humphreys. - The spectral lines of Humphreys series lie in infrared region. Hence, the correct answer is (d).