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Why does the atomic mass of chlorine (35.5) lie between two integers?
ABecause of rounding errors
BBecause chlorine has isotopes Cl-35 and Cl-37 in fixed ratio
CBecause chlorine has only fractional protons
DBecause chlorine has a half neutron
Answer & Solution
Correct answer: B. Because chlorine has isotopes Cl-35 and Cl-37 in fixed ratio
1. Chlorine has two stable isotopes: Cl-35 and Cl-37.
2. They occur in roughly 3 : 1 abundance.
3. The atomic mass is a weighted average of these masses.
4. The weighted average comes out near 35.5.
5. So the non-integer atomic mass reflects isotope abundance.
_Source: Selina Concise Chemistry ICSE Class 9, Ch 4 'Atomic Structure'_
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