Which of the following is NOT considered a greenhouse gas?

Oxygen is not considered a greenhouse gas because it does not have the ability to absorb and re-emit infrared radiation effectively. Greenhouse gases have specific molecular structures that allow them to interact with long-wave radiation emitted by the Earth's surface, which helps to trap heat in the atmosphere.

Carbon dioxide, methane, and water vapor all possess these properties, making them effective at contributing to the greenhouse effect. Carbon dioxide is produced from various sources including burning fossil fuels and is a significant contributor to warming. Methane is emitted during agricultural and industrial activities and is more effective than carbon dioxide at trapping heat. Water vapor, while a natural component of the atmosphere, serves as a key factor in the greenhouse effect as it can increase with temperature, further enhancing warming.

Therefore, oxygen, which primarily plays a role in respiration and does not contribute to the greenhouse effect, distinguishes itself from the other options listed.