Which one of the following is not a method to remove permanent hardness of water

Options

A. Clark's method
B. Calgon method
C. lon - exchange method
D. Synthetic resins method

Explanation

Clark's method is not used to remove permanent hardness of water. This method is used to remove temporary hardness of water.
`Ca(HCO_(3))_(2)+Ca(OH)_(2)rarr2CaCO_(3)darr+2H_(2)O`
`Mg(HCO_(3))_(2)+2Ca(OH)_(2)rarr2CaCO_(3)darrMg(OH)_(2)darr+2H_(2)O`
If excess of lime is added, water will again become hard because of adsorption of `CO_(2)` from the atmosphere.
`Ca(OH)_(2) + 2CO_(2) rarr Ca(HCO_(3))_(2)`