The first sentence is the correct sentence
Answer:
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1) N₂ (gas) ; that is, nitrogen (gas) ; (about 78%);
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and:
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2) O₂ (gas) ; that is, oxygen (gas); (about 21%);
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followed by argon, carbon dioxide, and others.
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Sword or axe. . . . . . . . . . . . .
