(N/A) The hydrogen spectral series refers to the set of discrete wavelengths of electromagnetic radiation emitted by hydrogen atoms when electrons transition between different energy levels. When an electron jumps from a higher energy level $(n_i)$ to a lower energy level $(n_f)$,a photon is emitted with energy $E = E_{n_i} - E_{n_f} = h\nu = \frac{hc}{\lambda}$.
The wavelength $\lambda$ is given by the Rydberg formula: $\frac{1}{\lambda} = R \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} \right)$,where $R$ is the Rydberg constant $(1.097 \times 10^7 \ m^{-1})$.
The main series are:
$1$. Lyman series: $n_f = 1$,$n_i = 2, 3, 4, \dots$ (Ultraviolet region).
$2$. Balmer series: $n_f = 2$,$n_i = 3, 4, 5, \dots$ (Visible region).
$3$. Paschen series: $n_f = 3$,$n_i = 4, 5, 6, \dots$ (Infrared region).
$4$. Brackett series: $n_f = 4$,$n_i = 5, 6, 7, \dots$ (Infrared region).
$5$. Pfund series: $n_f = 5$,$n_i = 6, 7, 8, \dots$ (Infrared region).