Permanent hardness in water cannot be cured by: boiling, ion exchange method, calgon's method, treatment with washing soda

The permanent hardness in water is due to the presence of sulphates and chlorides of calcium and magnesium. Permanent hardness in water cannot be cured by boiling. However, it can be cured by the ion exchange method, treatment with washing soda, Calgon's method and permit method. Hence, the correct option is A.