The atoms in a sample of an element are in excited states. A bright-line spectrum is produced when these atoms A. absorb energy B. absorb positrons C. emit energy D. emit positrons

The correct answer is C. To produce a bright-line spectrum, atoms will need to give off energy to then show this light. Emit means to give something off externally, so the answer is emit energy. A is incorrect because absorbing energy would be the opposite of C, because the atoms would be taking in rather than giving off light. Also, light is a form of energy, not a positron (which has the same mass as an electron but with a positive charge), making both B and D incorrect.