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The curie (Ci) was originally defined as the activity of what quantity of radium-226?
A1 kilogram of radium
B1 gram of radium
C1 mole of radium
D1 atom of radium
Answer & Solution
Correct answer: B. 1 gram of radium
1. The curie is a historical unit of activity, distinct from the SI becquerel.
2. It was defined as the activity of exactly 1 gram of radium-226.
3. A kilogram or a mole of radium-226 would represent a much larger activity than one curie.
4. A single atom's decay rate is far too small to define a practical unit like the curie.
5. So 1 gram is correct.
_Source: OpenStax Physics (CC BY 4.0), Ch 22 "The Atom", section 22.3 Half Life and Radiometric Dating_
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