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Topic Water hardness
Asked 3 times across 3 UPSC exams over 6 years (2020–2026), peaking in 2026.
Key insights
- Most tested in CAPF — 1 of 3 PYQs
- Most asked in 2026
- Recurs across 2 years (2020–2026)
How it travelled across exams
First appearance in each exam — the same idea, reframed.
CAPF 2020 → CDS 2026 → GEO 2026
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
Consider the following statements
- The temporary hardness in water is due to the presence of bicarbonates of calcium
- The permanent hardness in water is due to the presence of soluble chlorides and sulphates of calcium and magnesium
- The permanent hardness in water is removed by adding Na₂CO₃ to water
Which of the statements given above are correct ?
- A 1 and 2 only
- B 2 and 3 only
- C 1 and 3 only
- D 1, 2 and 3 ✓
✓ Correct answer: (D)
Science & Technology › Physics & Chemistry
GEO2026
Which of the following methods can be used for removing permanent hardness of water?
- Treatment with washing soda
- By ion exchange method
- By addition of lime
Select the correct answer using the code given below.
- A I and II
- B II only
- C I and III
- D I only
Answer key not yet available (pending official release)
Science & Technology › Physics & Chemistry
CAPF2020
Which one of the following methods can be used to remove permanent hardness of water?
- A Boiling
- B Ion-exchange ✓
- C Lime treatment
- D Bubbling sulphur dioxide gas
✓ Correct answer: (B)
Science & Technology › Physics & Chemistry
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