Question

• A. baking soda
• B. washing soda
• C. alum
• D. quick lime

Answer 1

The correct option is B

washing soda

Explanation for correct option:

(B) washing soda

• Addition of washing soda (Na₂CO₃) removes both permanent and temporary hardness of water.
• Bicarbonate salts as well as sulphates and chlorides salts undergo a double decomposition reaction with sodium carbonate (Na₂CO₃).
• In this reaction insoluble carbonates formed get precipitated and are removed by filtration.

$$\begin{gathered} \mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2+{\mathrm{Na}}_2{\mathrm{CO}}_3\to {\mathrm{CaCO}}_3\downarrow +2{\mathrm{NaHCO}}_3 \\ {\mathrm{MgSO}}_4+{\mathrm{Na}}_2{\mathrm{CO}}_3\to {\mathrm{MgCO}}_3\downarrow +{\mathrm{Na}}_2{\mathrm{SO}}_4 \\ {\mathrm{CaCl}}_2+{\mathrm{Na}}_2{\mathrm{CO}}_3\to {\mathrm{CaCO}}_3\downarrow +2\mathrm{NaCl} \end{gathered}$$

Explanation for incorrect option:

(A) Baking soda : Baking soda chemical name is Sodium hydrogen carbonate (NaHCO₃). It is used in baking industry and for reducing the acidity in the stomach.

(C) Alum:- It is an inorganic compound composed of water molecules, aluminium and other metals also like potash alum, aluminium alum etc The chemical formula of potash alum is KAl(SO₄)₂.12H₂O. It is used in the leather industry.

(D) Quick lime:- The chemical name of quick lime is CaO(Calcium Oxide). It is extensively used for medicinal purposes and insecticides.

Hence, (B) is the correct option.