Question

Assertion: Permanent hardness of water is removed by treatment with washing soda.
Reason: Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble carbonates.

• A. Both assertion and reason are true and reason is the correct explanation of assertion.
• B. Both assertion and reason are true but reason is not the correct explanation of assertion.
• C. Both assertion and reason are false.
• D. Assertion is true but reason is false.

Answer 1

The correct option is A Both assertion and reason are true and reason is the correct explanation of assertion.

Permanent hardness is due to the presence of chlorides and sulphates of calcium and magnesium. It can be removed by adding washing soda $\left(N{a}_{2}C{O}_3\right)$ which is soluble in water.
$MC{l}_2+N{a}_{2}C{O}_3\to MC{O}_3\downarrow +2NaClMS{O}_4+N{a}_{2}C{O}_3\to MC{O}_3\downarrow +N{a}_{2}S{O}_4$
$(M=MgorCa)$
Hard water forms insoluble compound (either calcium carbonate or magnesium carbonate) on reaction with washing soda. This insoluble compound is later filtered out.
Hence, option (a) is correct.