An emission spectrum of a gas shows a set of bright

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Problem

An emission spectrum of a gas shows a set of bright, well-defined lines rather than a continuous band. Which of the following explanations is most consistent with this observation? (a) Electrons in the gas emit only those wavelengths that can resonate with the mean free path of the atoms, producing discrete lines.Electrons\ in\ the\ gas\ emit\ only\ those\ wavelengths\ that\ can\ resonate\ with\ the\ mean\ free\ path\ of\ the\ atoms,\ producing\ discrete\ lines. (b) The bright lines result from Doppler shifts that separate a continuous spectrum into distinct wavelengths as atoms move at different speeds.The\ bright\ lines\ result\ from\ Doppler\ shifts\ that\ separate\ a\ continuous\ spectrum\ into\ distinct\ wavelengths\ as\ atoms\ move\ at\ different\ speeds. (c) Electrons in the gas can occupy only certain quantized energy states, so photons are emitted only with energies equal to differences between those states.Electrons\ in\ the\ gas\ can\ occupy\ only\ certain\ quantized\ energy\ states,\ so\ photons\ are\ emitted\ only\ with\ energies\ equal\ to\ differences\ between\ those\ states. (d) Only a few wavelengths are able to escape the gas without being re ⁣-absorbed, giving the illusion of an emission line spectrum.Only\ a\ few\ wavelengths\ are\ able\ to\ escape\ the\ gas\ without\ being\ re\!\text{-}absorbed,\ giving\ the\ illusion\ of\ an\ emission\ line\ spectrum.

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