Question

Assertion (A): Permanent hardness of water is removed by treatment with washing soda.
Reason(R): Washing soda reacts with soluble magnesium and calcium sulphate to form water-soluble compounds.

• A. (A) and (R) both are correct and (R) is the correct explanation of (A).
• B. (A) and (R) both are correct but (R) is not the correct explanation of (A).
• C. (A) is correct but (R) is not correct.
• D. (A) is not correct but (R) is correct.

Answer 1

The correct option is C

(A) is correct but (R) is not correct.

Permanent hardness is due to the presence of chlorides and sulphates of calcium and magnesium. It can be removed by adding washing soda (${\text{Na}}_2{\text{CO}}_3$), which is soluble in water.

Hard water forms insoluble compound (either calcium carbonate or magnesium carbonate) on reaction with washing soda. This insoluble compound is later filtered out. Hence, the assertion is correct but the reason is incorrect.