Which one of the following is not a main greenhouse gas ?
- (a)Water vapour
- (b)Oxygen
- (c)Carbon dioxide
- (d)Methane
Correct — B, Oxygen. Oxygen (O2) is a symmetric diatomic molecule that does not absorb infrared radiation, so it is not a greenhouse gas. Water vapour, carbon dioxide and methane all absorb outgoing infrared and are major greenhouse gases.
- (a)Water vapour — It is actually the most abundant greenhouse gas and a strong absorber of infrared radiation.
- (c)Carbon dioxide — A principal greenhouse gas whose rising concentration drives global warming.
- (d)Methane — A potent greenhouse gas, many times more effective than CO2 per molecule over the short term.
Greenhouse gases absorb and re-emit the infrared (heat) radiated by the Earth, warming the lower atmosphere. Molecules that can do this have asymmetric charge distributions or bending/stretching modes in the infrared — water vapour, CO2, methane, nitrous oxide, ozone. Symmetric diatomic gases like N2 and O2 cannot, so they are transparent to infrared.
The question asks for the NON-greenhouse gas. The main atmospheric gases nitrogen and oxygen are NOT greenhouse gases; the trace gases (CO2, CH4, water vapour) are.
- Main greenhouse gases: water vapour, CO2, methane, nitrous oxide, ozone.
- Oxygen and nitrogen are not greenhouse gases (symmetric diatomic molecules).
- Water vapour is the most abundant greenhouse gas.
- Methane is far more potent per molecule than CO2 over the short term.
- Assuming oxygen/nitrogen are greenhouse gases — they are not.
- Forgetting water vapour is a greenhouse gas.
Asked as which gas is NOT a greenhouse gas, or listing the main greenhouse gases.
No directly related past PYQ was found.
- practice — not a real PYQ
Which of the following is a greenhouse gas?
- (a)Nitrogen
- (b)Oxygen
- (c)Methane
- (d)Argon
Answer(c) Methane.
- practice — not a real PYQ
The most abundant greenhouse gas in Earth's atmosphere is
- (a)carbon dioxide
- (b)methane
- (c)water vapour
- (d)ozone
Answer(c) water vapour.