What distinguishes an emission spectrum from an absorption spectrum?

An emission spectrum is characterized by bright lines or bands on a dark background. This phenomenon occurs when atoms or molecules emit photons at specific wavelengths as electrons transition to lower energy levels. Each emitted photon corresponds to the energy difference between the two levels, and thus produces a bright line at that particular wavelength. This is typically due to gas excited by heat or other energy sources, which then releases energy in the form of light when returning to a lower energy state.

In contrast, an absorption spectrum occurs when light passes through a cooler gas. Certain wavelengths of light are absorbed by the gas as electrons in the atoms absorb energy and move to higher energy levels. This results in dark lines on a continuous spectrum; the dark lines mark the specific wavelengths that have been absorbed, hence appearing as gaps in the continuous spectrum.

The other options present variations or misconceptions about the definitions and visuals of these spectra. For instance, an emission spectrum does not display a complete or continuous color range, and while absorption spectra involve gases, they are not exclusive to them.