Question

The major constituent of air (by volume) is:

• A. Nitrogen
• B. Carbon dioxide
• C. Oxygen
• D. Hydrogen

Hint:

Air is mostly nitrogen, about 78 percent by volume.

Answer 1

The Correct Option is A

Think of air composition as a simple ratio you can memorize.

1. By volume, dry air is roughly $78\%$ nitrogen, $21\%$ oxygen, and about $1\%$ other gases including argon and carbon dioxide.
2. Among the four choices, nitrogen has by far the largest share.
3. Oxygen is essential for respiration and combustion but is still the second largest gas, not the majority one.
4. Carbon dioxide and hydrogen exist only in tiny trace amounts in air, so they cannot be the major constituent.
5. Hence the correct choice is option A, Nitrogen.