MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
What is the percentage of the ³⁵Cl isotope in nature?
Think it through first, then pick an option.
- a 25%
- b 33%
- c 66%
- d 75%
Answer and explanation
Correct answer: d 75%
(35 × 75 + 37 × 25)/100 = 35.5, so ³⁵Cl is 75%.
Why the other options are wrong
- a 25%: 25% is the share of ³⁷Cl; ³⁵Cl is 75%.
- b 33%: 33% does not fit; chlorine is 75% ³⁵Cl and 25% ³⁷Cl.
- c 66%: 66% does not fit; to average 35.5 the ³⁵Cl share must be 75%.
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