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

Step 1: Understanding the Question:
The question asks for the share of nitrogen gas in the atmosphere within the lowest 50 km from the ground, the region where air is well mixed.

Step 2: Key Formula or Approach:
Up to about 50 to 100 km, turbulent mixing keeps the mix of major gases nearly uniform. This zone is called the homosphere. Within it, nitrogen makes up close to 78% of the air by volume, oxygen makes up close to 21%, and the rest is argon, carbon dioxide and trace gases.

Step 3: Detailed Explanation:
Option (1), about 48% nitrogen, option (2), about 58%, and option (3), about 68%, all fall well short of the actual share nitrogen holds in the atmosphere.
Option (4), about 78% nitrogen, matches the well established figure for nitrogen's share in the well mixed lower and middle atmosphere, which stays essentially the same up to about 50 km.

Step 4: Final Answer:
Nitrogen makes up about 78% of the atmosphere up to 50 km, so option (4) is correct.