Using atomic masses C=12, O=16 g/mol, what percent by mass of C is in carbon monoxide (CO)?

A) 32.9%

B) 42.9%

C) 52.9%

D) 57.1%

Answer: B

Explanation: The formula mass is about 28 g/mol; C contributes 12 g per mole. Divide 12 by 28 and multiply by 100 to obtain about 42.9%.