Which one of the following gases is placed second in respect of abunda

Which one of the following gases is placed second in respect of abundance in the Earth’s atmosphere ?

Oxygen
Hydrogen
Nitrogen
Carbon dioxide
This question was previously asked in
UPSC NDA-2 – 2017
The Earth’s atmosphere is primarily composed of nitrogen (N₂) and oxygen (O₂). By volume, dry air contains approximately 78% nitrogen and 21% oxygen. The next most abundant gas is Argon (Ar), which makes up about 0.9%. Carbon dioxide (CO₂) is present in much smaller concentrations, around 0.04%. Hydrogen is present in trace amounts. Therefore, nitrogen is the most abundant gas, and oxygen is the second most abundant gas in the Earth’s atmosphere.
– Nitrogen (N₂) is the most abundant gas (approx. 78%).
– Oxygen (O₂) is the second most abundant gas (approx. 21%).
– Argon is the third most abundant (~0.9%).
The exact composition of the atmosphere can vary slightly with altitude, location, and the presence of moisture (water vapor is a significant component in humid air, but its concentration is highly variable). The balance of these gases is crucial for life on Earth and for regulating climate.