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Dry air is a mixture of gases whose volume percentage is about..
  • A
    19% oxygen, 80% nitrogen, 1% other gases.
  • B
    21% oxygen, 78% nitrogen, 1% other gases.
  • C
    25% oxygen, 74% nitrogen, 1% other gases.
  • D
    18% oxygen, 80% nitrogen, 2% other gases.

Composition of the Atmosphere

The atmosphere contains about 21% of oxygen. The other gases in the air are nitrogen, about 78%, and small amounts of carbon dioxide, water vapour and the rare gases such as argon. These volume percentages for each gases remain constant to about 70 000 ft - well within the altitudes at which conventional aircraft operate.

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