Which of the following gases is NOT considered a greenhouse gas?

Oxygen is not classified as a greenhouse gas because it does not absorb and re-emit infrared radiation in the atmosphere. Greenhouse gases, such as carbon dioxide, methane, and water vapor, possess molecular structures that allow them to interact with infrared radiation emitted by the Earth's surface. This interaction is essential for the greenhouse effect, which warms the planet by trapping heat in the atmosphere.

In contrast, oxygen primarily participates in combustion and respiration processes and does not have the necessary vibrational modes to absorb and release infrared radiation effectively. Therefore, while it is an essential gas for life on Earth, it does not contribute to the greenhouse effect like the other listed gases. Understanding the roles of different gases in climate dynamics is vital to grasping how human activities impact the Earth's atmosphere and climate change.