Which term refers to gases that trap heat in the atmosphere?

• A. Oxygen
• B. Greenhouse gas
• C. Nitrogen
• D. Helium

Answer: (B)

Gases that trap heat in the atmosphere are called greenhouse gases. They absorb infrared radiation emitted by Earth’s surface and re-emit energy back toward the surface, which helps keep the lower atmosphere warmer than it would be otherwise. This heat-trapping effect comes from molecular vibrations that interact with infrared wavelengths, so gases like water vapor, carbon dioxide, methane, nitrous oxide, and ozone contribute to warming. The other options—oxygen, nitrogen, and helium—don’t absorb infrared radiation strongly, so they don’t significantly trap heat in the atmosphere. That’s why the term greenhouse gas is the best fit.