Question

Which among these is not a greenhouse gas?

• A. Water vapour
• B. Carbon-dioxide
• C. Hydrogen
• D. Ozone

Hint:

Greenhouse gases play a major role in climate change by trapping heat in the atmosphere. Understanding them helps in addressing global warming.

Answer 1

The Correct Option is C

Step 1: Understanding greenhouse gases.
Greenhouse gases are gases that trap heat in the Earth's atmosphere, contributing to the greenhouse effect. Common greenhouse gases include carbon dioxide (CO₂), methane (CH₄), water vapour (H₂O), and ozone (O₃).

Step 2: Analyzing the options.
(A) Water vapour: Water vapour is a greenhouse gas.
(B) Carbon-dioxide: Carbon-dioxide is a major greenhouse gas.
(C) Hydrogen: Correct — Hydrogen is not considered a greenhouse gas.
(D) Ozone: Ozone is a greenhouse gas that exists in the Earth's atmosphere.

Step 3: Conclusion.
The correct answer is (C) Hydrogen, as it is not a greenhouse gas.

Answer 2

Whether a gas is a greenhouse gas depends on a specific physical property: whether its molecules can absorb and re-emit infrared (heat) radiation, which in turn depends on the molecule having an asymmetric structure or more than two atoms that can vibrate in ways that interact with IR light.

1. Water vapour: A bent, asymmetric molecule (H2O) that vibrates in ways that strongly absorb infrared radiation, making it a very effective greenhouse gas.
2. Carbon-dioxide: A linear but flexible molecule (CO2) whose bending and stretching vibrations absorb infrared radiation strongly, making it one of the principal greenhouse gases.
3. Hydrogen: A simple, symmetric diatomic molecule (H2) made of two identical atoms, which has no dipole moment and essentially does not absorb infrared radiation, so it cannot trap heat the way greenhouse gases do.
4. Ozone: A bent, triatomic molecule (O3) that absorbs both ultraviolet and infrared radiation, making it a recognized greenhouse gas as well as a UV shield.

Since hydrogen's simple, symmetric two-atom structure means it does not trap infrared heat the way the other three molecules do, it is the one gas here that is not a greenhouse gas.

Therefore, the correct answer is Hydrogen.