Question
Which one of the following salts is responsible for temporary hardness of water?
NDA
General Ability
General Science
2025
NDA 2025 (Phase 2)
NDA General Ability Question (2025) — Solution
Options
- A. Sulphates of calcium
- B. Chlorides of magnesium
- C. Bicarbonates of magnesium
- D. Sulphates of magnesium
Answer
C. Bicarbonates of magnesium
Step-by-step solution
Temporary hardness of water is caused by the presence of dissolved bicarbonates of calcium and magnesium, namely Ca(HCO_3)_2 and Mg(HCO_3)_2. Permanent hardness of water is caused by the presence of dissolved chlorides and sulphates of calcium and magnesium. Therefore, bicarbonates of magnesium are responsible for the temporary hardness of water. Answer: Bicarbonates of magnesium
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