Which type of spectrum is identified by dark lines on a continuous background?

• A. Emission line spectrum
• B. Continuous spectrum
• C. Line spectrum
• D. Absorption line spectrum

Answer: (D)

When light from a hot, dense source is spread into a spectrum, you get a continuous rainbow with all wavelengths present. If that light then passes through a cooler, diffuse gas, atoms in the gas absorb photons at specific wavelengths that match their electronic transitions. Those absorbed wavelengths appear as dark gaps in the otherwise smooth, continuous spectrum. The pattern you’re seeing is an absorption line spectrum: dark lines set against a continuous background. This contrasts with an emission line spectrum, which shows bright lines on a dark background when the gas itself emits at particular wavelengths, and with a purely continuous spectrum, which has no lines at all.