Question

Which of the following is not a greenhouse gas?
A. Carbon dioxide
B. Water vapour
C. Oxygen
D. Methane

Answer 1

Hint: The increase of the greenhouse gases in the earth atmosphere is the reason for global warming which is a popular and globally occurring phenomenon caused by human activities. Oxygen is not one of those gases.

Complete step by step solution:
Every gas in the atmosphere based on the environmental conditions on the planet has its range in the electromagnetic (EM) spectrum where it absorbs the radiation. This means that certain gases are opaque to certain parts of the EM radiation because it absorbs in that part of the radiation. For earth, the Sun is the ultimate source of energy for all the atmospheric and oceanic flows that we observe and experience. Then the next source is earth’s own radiation. Now a major part of the sun’s energy is concentrated in the visible range of the EM spectrum. Our earth emits radiation concentrated in the infrared region of the EM spectrum. Since most of the gases are transparent to the visible light, we only sense the gases through wind, or particles. Now gases like carbon dioxide, water vapour, methane and other examples are known as greenhouse gases for a reason. These absorb radiation in the infrared region of the EM spectrum. Since the earth radiates in the infrared region, the presence of these gases do not allow infrared radiation to escape to outer space and warms the atmosphere instead. Just like the glass of greenhouse traps heat inside the structure to keep the environment inside warm, these gases keep the atmosphere warm. The molecular structure and environmental conditions decide the absorptivity of the gas. Oxygen is neutral to this part of the spectrum and thus our answer to the above question. Thus we can say that option C is correct.

Note: Carbon dioxide has risen to popularity due to the global warming issue. It is not a bad gas in the environment, it is the quantity of these gases that play a role in maintaining the suitable temperature of the planet. If the quantity of gases decreases, the planet would freeze out life.