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Hard water contains dissolved salts such as magnesium and calcium chlorides, bicarbonates, or sulfates. It has two types of hardness: temporary hardness and permanent hardness. Which of the following methods can remove temporary hardness of water?
- Boiling hard water
- Adding slaked lime (Ca(OH)2)
- Adding dilute H2SO4
- Adding milk of magnesia
Correct answer: Boiling hard water
Solution
Temporary hardness is due to Ca(HCO3)2 and Mg(HCO3)2. It can be removed by: (1) Boiling -- bicarbonates decompose to insoluble carbonates. (2) Clark's process -- adding calculated amount of Ca(OH)2. Options C (H2SO4) and D (Mg(OH)2) do not remove temporary hardness. Among the listed options, boiling is the simplest and most direct method to remove temporary hardness only (not permanent). Adding slaked lime (Clark's process) also removes temporary hardness but can be tricky as excess lime causes new hardness. The question says 'which can remove temporary hardness' -- both A and B are correct methods. However in most NCERT/JEE contexts, boiling is the primary answer for temporary hardness removal.
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