Final answer:
Carbon dioxide absorbs the most heat energy during sublimation, which is the change from a solid to a gaseous state without becoming a liquid.
Step-by-step explanation:
When considering the question, "When does carbon dioxide absorb the most heat energy?" the answer is during the phase change known as sublimation. Sublimation is the transition of a solid directly into a gas phase, without passing through the intermediate liquid phase. This process requires a significant amount of heat energy to overcome the solid's lattice energy and allow the molecules to move apart to form a gas. Examples of sublimation include the transition of dry ice, which is solid carbon dioxide, directly into carbon dioxide gas at room temperature and standard pressure. The correct answer to the question is C) during sublimation.