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An organic compound has the composition 38.8% carbon, 16.0% hydrogen, and 45.2% nitrogen by mass. Which molecular formula matches this compound?

1. CH₃NH₂
2. CH₃CN
3. C₂H₅CN
4. CH₂(NH₂)₂

Correct answer: CH₃NH₂

Solution

Moles C:H:N = 38.8/12 : 16/1 : 45.2/14 = 1 : 5 : 1, giving CH5N = CH3NH2 (which matches the percentages exactly). The stored CH2(NH2)2 does not fit.

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