Final answer:
Chlorofluorocarbons (CFCs) have the greatest ability to absorb heat on a per-mole basis among the options listed due to their high global warming potential and long atmospheric lifetime. Methane is also highly potent, but CFCs are superior in terms of per-mole heat absorption.
Step-by-step explanation:
The student asked which atmospheric constituent has the greatest ability to absorb heat on a per-mole basis. Among the options provided — ozone (O3), methane (CH4), water vapor (H2O), chlorofluorocarbons (CFCs), and carbon dioxide (CO2) — CFCs demonstrate the highest global warming potential (GWP), making them the most potent on a per-mole basis for absorbing heat. This is due to their long atmospheric lifetime and strong efficiency at trapping heat. Methane is also a very potent greenhouse gas, approximately 28 times more effective than CO2 at absorbing infrared radiation, although it is present in the atmosphere at lower concentrations and has a shorter lifespan compared to CO2 or CFCs. CO2, while less effective per mole compared to CFCs or methane, is the most abundant and persists longer in the atmosphere, making it a major contributing factor to the greenhouse effect. However, in terms of absorption ability per mole, CFCs outperform the other constituents listed.