Answer:
C) an emission line spectrum.
Explanation:
In simple terms the process happening here is that electrons are move from a state of higher energy levels to a state of lower energy levels.
Emission line spectrum are spectrum that appear when atoms or molecules return to their normal configuration from an excited state. They usually release the absorbed energy in the form of radiation.
In the question the heating of the gas is evident that the gas was put into an excited state and then it returns to its normal state
