Molecules of Carbon Dioxide in a Sample

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Carbon dioxide comprises, on average, about 397 parts per million of the Earth's atmosphere, on a molecular basis. In an even sample of the Earth's atmosphere consisting of 4 billion molecules, approximately how many of those molecules would be expected to be carbon dioxide? (1 billion = 1,000,000,000)

Review: Molecules of Carbon Dioxide in a Sample


Explanation

In this question, we are working with a ratio that doesn't change, so we can write two instances of this ratio and set them equal:



Counting zeroes:



We can cross-multiply and solve:





Hearing "approximately" and seeing the answer choices, we can take .





The correct answer is (C).


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