Question

Which one or more of the following is/are greenhouse gas(es)? 

• A. Methane
• B. Water vapour
• C. Sulphur dioxide
• D. Nitrous oxide

Hint:

Common greenhouse gases to remember for GATE Ecology: {CO$_2$, CH$_4$, N$_2$O, and H$_2$O}. Gases like SO$_2$ mainly cause cooling via aerosols, not greenhouse warming.

Answer 1

The Correct Option is A, B, D

Step 1: Clarify what greenhouse gases are. 
Greenhouse gases are components of the atmosphere that have the ability to absorb and re-emit infrared radiation.
By doing so, they retain heat within the Earth’s atmosphere and are responsible for the greenhouse effect.

Step 2: Examine option (A) — Methane.
Methane (CH$_4$) is a powerful greenhouse gas with a much higher warming impact per molecule than carbon dioxide.
Its strong absorption of infrared radiation makes it an important contributor to global warming.
Therefore, option (A) is correct.

Step 3: Examine option (B) — Water vapour.
Water vapour (H$_2$O) is the most prevalent greenhouse gas in the atmosphere.
It plays a key role in Earth’s climate system by efficiently trapping outgoing infrared radiation and regulating temperature.
Hence, option (B) is correct.

Step 4: Examine option (C) — Sulphur dioxide.
Sulphur dioxide (SO$_2$) mainly forms aerosols in the atmosphere, which reflect incoming sunlight and produce a cooling effect.
It does not significantly absorb infrared radiation and is not classified as a greenhouse gas.
Thus, option (C) is incorrect.

Step 5: Examine option (D) — Nitrous oxide.
Nitrous oxide (N$_2$O) is a long-lived and highly effective greenhouse gas.
Its ability to absorb infrared radiation allows it to contribute substantially to atmospheric warming.
Therefore, option (D) is correct.

Step 6: Final conclusion.
Among the given choices, the gases that function as greenhouse gases are:

\[ \boxed{(A),\ (B)\ \text{and}\ (D)} \]