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When a nucleus emits an alpha particle, how do its mass number and atomic number change?
ABoth mass number and atomic number stay unchanged
BMass number stays same and atomic number rises by 1
CMass number falls by 2 and atomic number by 4
DMass number falls by 4 and atomic number by 2
Answer & Solution
Correct answer: D. Mass number falls by 4 and atomic number by 2
1. An alpha particle is a helium nucleus with mass number 4 and atomic number 2.
2. By Soddy-Fajan's law, emitting it lowers the mass number by 4.
3. It also lowers the atomic number by 2.
4. Option B describes beta decay, not alpha decay.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 6 Nuclear Physics "Nuclear Physics", p.84_
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