Question

Assertion (A): Washing soda is used for washing clothes in hard water.
Reason (R): Washing soda can remove hardness of water.

• A. A is true but R is false
• B. A is False but R is true
• C. Both A and R are true and R is the correct explanation of A
• D. Both A and R are true and R is not the correct explanation of A

Answer 1

The correct option is C Both A and R are true and R is the correct explanation of A

Hardness of water is due to the presence of chlorides and sulphates of calcium and magnesium. It can be removed by adding washing soda (${\text{Na}}_2{\text{CO}}_3$). The reaction involved is:

$CaC{l}_2\left(aq\right)+N{a}_{2}C{O}_3\left(aq\right)\to CaC{O}_3\left(s\right)+2NaCl\left(aq\right)$

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 and reason both are correct.