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In a healthy adult human body, the most abundant elements by mass are oxygen (61.4%), carbon (22.9%), hydrogen (10.0%), and nitrogen (2.6%). If every 1H atom in a 75 kg person were replaced by 2H atoms, by how much would the person's mass increase?

1. 15 kg
2. 37.5 kg
3. 7.5 kg
4. 10 kg

Correct answer: 7.5 kg

Solution

Replacing each hydrogen atom with two deuterium atoms effectively doubles the mass contribution from hydrogen. Since hydrogen makes up about 10% of a 75 kg person, this results in an increase of approximately 7.5 kg.

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