alleryStart learning →The unified atomic mass unit is defined as exactly one twelfth of the mass of one atom of:
AHydrogen-1
BHelium-4
CCarbon-12
DOxygen-16
Answer & Solution
Correct answer: C. Carbon-12
1. Chemists needed a mass unit scaled to single atoms rather than to grams.
2. The unified atomic mass unit is defined as exactly 1/12 of the mass of a single atom of the carbon-12 isotope.
3. It is equal to 1.6605 times ten to the minus 24 grams.
4. Oxygen-16 served as the standard historically but is not the current definition.
_Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 2 'Atoms, Molecules, and Ions', sections 2.1-2.6_
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