Using Bohr's postulates, derive the expression for the frequency of radiation emitted when electron in hydrogen atom undrgoes transition from higher energy state (quantum number `n_i`) to the lower state (`n_f`).
When electron in hydrogen atom jumps from energy state `n_i=4` to `n_f=3,2,1` , identify the spectral series to which the emission lines belong.

Explanation

`4 to 1` transition: the emission line belongs to the Lyman series.
`4 to 2` transition: the emission line belongs to the Balmer series.
`4 to 3` transition: the emission line belongs to the Paschen series.