(1) What is meant by line spectra of atom ?
(2) How many lines are observed in the visible region of hydrogen spectrum?

Explanation

(1) When electric discharge is passed through a gaseous element enclosed in a discharge tube under low pressure and the emitted light is analysed by a spectroscope, the spectrum consists of a large number of lines (with different frequencies) which are grouped into different series. the complete spectrum so obtained is known as line spectra or atomic spectra.
(2) In the visible region of hydrogen spectrum, four lines are obtained: `H_(alpha)` [red], `H_(beta)` [bluish green], `H_(gamma)` (blue) and `H_(delta)` (violet). the series consisting of these lines is called Balmer series.