CSET Multiple Subjects Subtest 2 Math And Science Practice Test

Which gas primarily makes up Earth's atmosphere?

Nitrogen Oxygen Argon Carbon Dioxide

Correct Answer:

Nitrogen

Explanation:

Earth's atmosphere is a mixture of gases, and the largest portion by volume is nitrogen. About 78% of dry air is nitrogen (N2), making it the dominant component. The next major gas is oxygen, which is around 21%. The remaining gases—argon, carbon dioxide, neon, helium, methane, and others—are present only in trace amounts, together contributing less than a few percent. Nitrogen is so abundant because it is quite unreactive under surface conditions, so it stays in the atmosphere for long periods while other gases cycle more quickly. This stability lets nitrogen maintain its lead as the primary gas in Earth's atmosphere.

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