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Topic

Hardness of water

Asked 2 times in CDS over 3 years (2015–2018), peaking in 2015.
2
PYQs
1
Exams
2
Years active
2015–2018
Span
2015
Peak
2/2
Answers
📅 Full chronological timeline →

Key insights

  • Most tested in CDS — 2 of 2 PYQs
  • Most asked in 2015
  • Recurs across 2 years (2015–2018)

Across exams

CDS · 2

How the concept evolved

115
118
Long-running — most appearances (1 of 2) predate 2016, and it still returns.

Sample questions

You've seen the pattern — here are a few of the actual PYQs.
CDS2018

Which of the following substances cause temporary hardness in water?

  1. Mg(HCO3)2
  2. Ca(HCO3)2
  3. CaCl2
  4. MgSO4

Select the correct answer using the code given below.

  1. A 3 and 4
  2. B 2 and 3
  3. C 1 and 4
  4. D 1 and 2 ✓
✓ Correct answer: (D)
Science & Technology › Physics & Chemistry
CDS2015

When hard water is evaporated completely, the white solid remains in the container. It may be due to the presence of

  1. Carbonates of Ca and Mg
  2. Sulphates of Ca and Mg
  3. Chlorides of Ca and Mg

Select the correct answer using the code given below :

  1. A 1 and 2 only
  2. B 1, 2 and 3 ✓
  3. C 3 only
  4. D 1 and 3 only
✓ Correct answer: (B)
Science & Technology › Physics & Chemistry

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