Using rounded atomic masses, what percent by mass of K is in potassium nitrate (KNO3)?

A) 61.4%

B) 38.6%

C) 48.6%

D) 28.6%

Answer: B

Explanation: The formula mass is about 101 g/mol; K contributes 39 g per mole. Divide 39 by 101 and multiply by 100 to obtain about 38.6%.

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