Final answer:
Discrete spectral lines are produced when a gas is excited by electrical current or heat, resulting in a unique set of line spectra that represent the quantized energy states of the atoms.
Step-by-step explanation:
Discrete spectral lines occur when excitation takes place in a gas. When a gas is excited at low partial pressure using an electrical current, or by heating it, a line spectrum is produced. This phenomenon is related to the discrete energies emitted by the gas reflecting the quantized energy states of the atoms within it.
An example of this is seen with fluorescent light bulbs and neon signs. Each element and to a more complicated degree each molecule has a unique set of spectral lines that can serve as a powerful analytical tool.