Permanent hardness is due to presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water. Permanent hardness of water can be removed by

Options

A. boiling
B. Clark's method
C. treatment with sodium carbonate
D. treatment with 2-ethylanthraquinol in the presence of air.

Answer

C

Explanation

Permanent hardness can not be removed by boiling or by the addition of slaked lime. Water softners which are used to remove permanent hardness are washing soda (sodium carbonate), permutit, calgon, etc.