Which of the following contributes most significantly to the greenhouse effect on Earth?
Correct: C
While N₂ and O₂ are the most abundant gases in the atmosphere, they are largely transparent to infrared radiation and do not significantly contribute to the greenhouse effect. CO₂, though present in much smaller concentrations (~0.04%), is a major greenhouse gas because it absorbs and re-emits infrared radiation, trapping heat in the atmosphere. Other greenhouse gases include methane (CH₄), water vapor, and nitrous oxide (N₂O), but CO₂ is the most significant anthropogenic greenhouse gas driving global warming.