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Topic Chemical formulae
Asked 3 times across 2 UPSC exams over 6 years (2020–2026), peaking in 2020.
Key insights
- Most tested in CDS — 2 of 3 PYQs
- Most asked in 2020
- Recurs across 3 years (2020–2026)
How it travelled across exams
First appearance in each exam — the same idea, reframed.
CDS 2020 → CISF 2024
How the concept evolved
Rising — more than half its appearances (3 of 3) are since 2016.
Sample questions
You've seen the pattern — here are a few of the actual PYQs.
CDS2026
Which one among the following pairs of compound and chemical formula is not correctly matched ?
- A Bleaching powder : CaOCl₂
- B Soda ash : Na₂CO₃
- C Baking powder : NaHCl₂ ✓
- D Plaster of Paris : 2CaSO₄·H₂O
✓ Correct answer: (C)
Science & Technology › Physics & Chemistry
CISF2024
The chemical formula of washing soda is
- A NaHCO3
- B Na2CO3
- C Na2CO3·10H2O ✓
- D NaOCl
✓ Correct answer: (C)
Science & Technology › Physics & Chemistry
CDS2020
Match List-I with List-II and select the correct answer using the code given below the Lists
| List I (Name) | List II (Formula) |
|---|
| A. Bleaching powder | 1. NaHCO₃ |
| B. Baking soda | 2. Na₂CO₃·10H₂O |
| C. Washing soda | 3. Ca(OH)₂ |
| D. Slaked lime | 4. CaOCl₂ |
Codes:
- A A-4 B-1 C-2 D-3 ✓
- B A-4 B-2 C-1 D-3
- C A-3 B-2 C-1 D-4
- D A-3 B-1 C-2 D-4
✓ Correct answer: (A)
Science & Technology › Physics & Chemistry
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