Question

The concentration of nitrogen in atmosphere upto 50 km from the ground surface is

• A. About 48% nitrogen
• B. About 58% nitrogen
• C. About 68% nitrogen
• D. About 78% nitrogen

Hint:

Recall the standard composition figures for nitrogen and oxygen in the well mixed lower atmosphere.

Answer 1

The Correct Option is D

This question checks the basic composition of air in the part of the atmosphere where gases stay evenly mixed.

1. About 48% nitrogen: Far too low; this is not close to nitrogen's real share.
2. About 58% nitrogen: Still well under the true figure.
3. About 68% nitrogen: Closer, but still short of the accepted value.
4. About 78% nitrogen: This matches the standard textbook figure. In the well mixed part of the atmosphere, up to roughly 50 to 100 km, nitrogen holds close to 78% by volume, with oxygen at about 21% and the remainder split between argon, carbon dioxide and trace gases.

Since air stays well mixed up to 50 km, the nitrogen share there matches the overall atmospheric figure of about 78%.

Let's summarize:

• The atmosphere below about 50 to 100 km is called the homosphere, where major gases stay in a fixed ratio.
• Nitrogen: about 78%, oxygen: about 21%, with small shares of argon and carbon dioxide.

So option (4), about 78% nitrogen, is correct.