Final answer:
Chlorofluorocarbons (CFCs) have the greatest ability to absorb heat on a per-mole basis among the listed atmospheric constituents, due to their high global warming potential.
Step-by-step explanation:
The student asked which atmospheric constituent has the greatest ability to absorb heat on a per-mole basis. The options were carbon dioxide (CO2), chlorofluorocarbons (CFCs), methane (CH4), ozone (O3), and water vapor (H2O). Based on the global warming potential (GWP), which measures the ability of greenhouse gases to absorb and re-radiate infrared energy, we can determine that chlorofluorocarbons (CFCs) generally have the highest GWP and thus the greatest ability to absorb heat per mole. This is largely due to their very long residence time in the atmosphere. Even though water vapor is a dominant player in the overall greenhouse effect and methane is a more potent greenhouse gas on a per-molecule basis compared to CO2, CFCs have a significantly higher GWP due to their chemical structure and longevity in the atmosphere.