Question:
Permanent hardness of water cannot be removed by
Permanent hardness of water cannot be removed by
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\textbf{Temporary hardness} \(\rightarrow\) Removed by boiling.
\textbf{Permanent hardness} \(\rightarrow\) Removed by washing soda, zeolite (Permutit), Calgon or ion-exchange methods.
Updated On: Jul 9, 2026
- Using \(\mathrm{Na_2CO_3}\)
- Using Calgon
- Using \(\mathrm{NaAlSiO_4}\)
- Boiling \bigskip
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The Correct Option is D
Solution and Explanation
Concept:
Permanent hardness is caused by chlorides and sulphates of calcium and magnesium. It cannot be removed by boiling because these salts do not decompose on heating.
Step 1: Analyse the methods.
• \(\mathrm{Na_2CO_3}\) removes permanent hardness by precipitating calcium and magnesium carbonates.
• Calgon removes hardness by complex formation.
• \(\mathrm{NaAlSiO_4}\) (zeolite) exchanges ions and softens water.
• Boiling removes only temporary hardness.
Step 2: Final conclusion. Therefore, \[ \boxed{\text{Permanent hardness cannot be removed by boiling}.} \] Hence, the correct option is \(\boxed{(D)}\).
Step 1: Analyse the methods.
• \(\mathrm{Na_2CO_3}\) removes permanent hardness by precipitating calcium and magnesium carbonates.
• Calgon removes hardness by complex formation.
• \(\mathrm{NaAlSiO_4}\) (zeolite) exchanges ions and softens water.
• Boiling removes only temporary hardness.
Step 2: Final conclusion. Therefore, \[ \boxed{\text{Permanent hardness cannot be removed by boiling}.} \] Hence, the correct option is \(\boxed{(D)}\).
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