Question

explain hydrogen spectrum?

Answer 1

When unexcited, hydrogen's electron is in the first energy level—the level closest to the nucleus. ... Hydrogen molecules are first broken up into hydrogen atoms and electrons are then promoted into higher energy levels.

Answer 2

The emission spectrum of atomic hydrogen has been divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two energy levels in an atom.