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Weather theoryQuestion 301 of 934

Which gas makes up the largest part of the atmosphere?

  1. Nitrogen, at 78 percent
  2. Oxygen, at 78 percent
  3. Argon, at 21 percent
  4. Carbon dioxide, at 21 percent
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Correct answer: Nitrogen, at 78 percent

Nitrogen accounts for 78 percent of the air. Oxygen makes up 21 percent.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 12: Weather Theory — Composition of the Atmosphere, page 286

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Questions last reviewed: 18 October 2026