Match the column I with column II and mark the appropriate choice. Column I Column II (A) Clark’s method (i) Na₆P₆O₁₈ (B) Calgon’s method (ii) NaAlSiO₄ (C) Ion-exchange method (iii) RSO₃H (D) Synthetic resins method (iv) Ca(OH)₂

On the addition of calcium hydroxide (slaked lime), the temporary hardness of water caused by calcium bicarbonate can easily be removed. This is called as Clark’s method. Calgon is the complex salt of sodium with formula 3 6 ( ) NaPO . It is used to remove hardness of water. Hydrated sodium aluminium silicates are used in ion exchange method to remove hardness of water. Also, 3 RCOOH and RSO H are used in synthetic resin methods.