Question

Why large no. Of lines appear in the spectrum of hydrogen although it contains only one electron?

Answer 1

Every element has very latge number of spectral lines, not just hydrogen. Each electron can be in infinite number of states, so, actually atoms have infinite number of spectral lines​ spread throughout the spectrum. If the electron jumps from n2 = 5 to n1 = 1 then following are the transitions possible. Hence there are 10 transitions and hence 10 spectral lines possible.

Answer 2

Answer:

Although hydrogen has only one electron, it contains many energy levels. When its electron jumps from higher energy level to a lower one, it releases a photon. Those photons cause different colours of light of different wavelengths due to the different levels. Those photons appear as lines.