Using rounded atomic masses, what percent by mass of C is in propane (C3H8)?

A) 81.8%

B) 18.2%

C) 91.8%

D) 71.8%

Answer: A

Explanation: The formula mass is about 44 g/mol; C contributes 36 g per mole. Divide 36 by 44 and multiply by 100 to obtain about 81.8%.

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