What do the spectral lines represent?

Question

What do the spectral lines represent?

Spectral lines is defined by quantum mechanics in terms of energy levels of ions, molecules, and atoms. When electrons move from a higher level to lower one, photons are emitted and an emission line can be seen in the spectrum. As electrons jump down to the n=2 orbit, they emit photons of specific frequency (hence colour) that can be seen as emission lines in the visible part of spectrum.

Explanation: