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

Step 1: Recall the composition of dry air by volume.
Air is a mixture of gases. Nitrogen makes up about 78 percent, oxygen about 21 percent, and the rest, less than 1 percent, is argon, carbon dioxide and other trace gases.

Step 2: Compare the given options.
Nitrogen (78 percent) is far higher than oxygen (21 percent), carbon dioxide (about 0.04 percent) and hydrogen (negligible, only trace amounts).

So option A, Nitrogen, is the major constituent of air.

Why the others are wrong: Oxygen is the second largest component, not the largest, so option C is wrong. Carbon dioxide and hydrogen are present only in trace amounts, they cannot be called major constituents, so options B and D are wrong.