Topic Isotopes
Asked 12 times across 5 UPSC exams over 45 years (1980–2025), peaking in 2020.
Key insights
- Most tested in NDA — 4 of 12 PYQs
- Most asked in 2020
- Recurs across 9 years (1980–2025)
How it travelled across exams
First appearance in each exam — the same idea, reframed.
CSE 1980 → CDS 2014 → CAPF 2015 → NDA 2020 → GEO 2025
How the concept evolved
180
191
114
115
116
220
221
224
125
Rising — more than half its appearances (8 of 12) are since 2016.
Related concepts
Ideas UPSC tests alongside this one — keep exploring.
Sample questions
You've seen the pattern — here are a few of the actual PYQs.
GEO2025
Separation of the isotope of uranium requires a physical method rather than a chemical method. It is so mainly because
- A it is too dangerous to mix other chemicals with uranium
- B the isotopes are chemically the same element ✓
- C the isotopes differ in number of neutrons
- D natural uranium contains only 0·7% U-235
✓ Correct answer: (B)
Science & Technology › Physics & Chemistry
CDS2024
The two isotopes of elemental chlorine are :
- A ³⁵₁₇C and ³⁶₁₇C
- B ³⁴₁₇C and ³⁶₁₈C
- C ³⁵₁₇C and ³⁷₁₈C
- D ³⁵₁₇C and ³⁷₁₇C ✓
✓ Correct answer: (D)
Science & Technology › Physics & Chemistry
NDA2024
The relative atomic mass of boron (which exists in two isotopic forms 10B and 11B) is 10.81. What will be the abundance of 10B and 11B, respectively (consider a sample of 100 atoms)?
- A 19% and 81% ✓
- B 81% and 19%
- C 38% and 62%
- D 62% and 38%
✓ Correct answer: (A)
Science & Technology › Physics & Chemistry
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