Permanent hardness in water is due to the presence of the following salts:
A. Calcium bicarbonate B. Magnesium bicarbonate C. Magnesium chloride D. Calcium nitrate E. Calcium sulphate
Choose the correct answer from the options given below:

Correct option is C

Water hardness is classified into two types: temporary hardness and permanent hardness.
· Temporary hardness is caused by bicarbonates of calcium and magnesium, which can be removed by boiling.
· Permanent hardness is due to the presence of sulfates, chlorides, and nitrates of calcium and magnesium, which cannot be removed by boiling.
Salts responsible for permanent hardness:
· Magnesium chloride (MgCl₂) – A highly soluble salt that contributes to permanent hardness.
· Calcium nitrate (Ca(NO₃)₂) – A salt that remains dissolved in water, causing permanent hardness.
· Calcium sulfate (CaSO₄) – A non-volatile salt that does not break down upon heating, leading to permanent hardness.
Salts that cause temporary hardness:
· Calcium bicarbonate (Ca(HCO₃)₂) – Causes temporary hardness and can be removed by boiling.
· Magnesium bicarbonate (Mg(HCO₃)₂) – Also causes temporary hardness and can be removed by heating.
Thus, the correct answer is (c) C, D, and E only.
Information Booster:
How to Remove Permanent Hardness?
1. Ion-Exchange Method – Using resins to replace calcium and magnesium ions with sodium ions.
2. Adding Washing Soda (Na₂CO₃) – Converts calcium and magnesium salts into insoluble precipitates.
3. Chelating Agents (e.g., EDTA) – Binds with metal ions, preventing scale formation.

Additional Knowledge:
· (a) A, B, and C only – A and B cause temporary hardness.
· (b) B, C, and D only – B (magnesium bicarbonate) causes temporary hardness.
· (d) A, D, and E only – A (calcium bicarbonate) causes temporary hardness.