Which of the following is NOT a greenhouse gas?

Oxygen is not considered a greenhouse gas because it does not have the ability to trap heat in the atmosphere. Greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, are characterized by their molecular structures that allow them to absorb and emit infrared radiation, contributing to the greenhouse effect. This phenomenon is fundamental to understanding climate change, as greenhouse gases retain heat from the Earth's surface, warming the atmosphere.

In contrast, oxygen is a diatomic molecule composed of two oxygen atoms. While it is essential for life and plays a crucial role in respiration and combustion, it does not have the same heat-trapping properties as the other gases listed. Therefore, it does not contribute to the greenhouse effect and is not classified as a greenhouse gas.