The major greenhouse gas is:
B. $CO_2$

Answer Verified Verified
Hint: Greenhouse gases are gases that are responsible for global warming by virtue of its ability to exhibit the greenhouse phenomenon.

Complete answer: A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range of the light spectrum. They cause the greenhouse effect on planets.
They are produced naturally, but the effect is neutralized by the ecological balance (by plants. When produced in excess, the balance is disturbed and this results in global warming. Human activities play a major role in the production of greenhouse gases
Out of all the contributing gases for the greenhouse effect, carbon dioxide ($CO_2$) is the most influential. Carbon dioxide emissions consist of 80-83% of the total greenhouse gas emissions. It is followed by nitrous oxide (NO) and fluorinated gases like chlorofluorocarbons (CFCs).

Additional information: Greenhouse effect results in the following:
1. Rise in the sea levels.
2. Changes in the thickness and nature of the ozone layer.
3. Increase in oceanic temperature resulting in the bleaching of coral and hence decrease in biodiversity.
4. Desertification of arable land.
5. Worsening of health amongst the human population. Increased incidence of respiratory diseases in the young and old.
6. Disruption of the water cycle, etc.

Correct answer is, Option 2.

Note: Chlorofluorocarbons (CFCs) are released from refrigerators, air conditioners, and air fresheners. They deplete the ozone layer (decreasing its thickness) by forming free radicals. Their depleting effect is long last and debilitating.
Nitrous oxide (NO) is another ozone layer destroyer produced by fossil fuel combustion, etc.