Question

multiple choice question
in order to produce an absorption - line spectrum, light from a source emitting a continuous spectrum must

pass through a cool gas cloud
be absorbed by the surface of a star
move an electron in an atom closer to its nucleus
pass through a vacuum

Explanation:

Absorption - line spectra are produced when light from a source with a continuous spectrum passes through a cooler gas. The atoms in the gas absorb specific wavelengths of the light, creating dark lines in the spectrum. Absorption by a star's surface doesn't create an absorption - line spectrum in the described context. Moving an electron closer to the nucleus is an effect rather than the cause of an absorption - line spectrum. Passing through a vacuum doesn't cause absorption - line spectra.

Answer:

A. pass through a cool gas cloud