Which one of the following is used for water softening?
A
Mg(HCO<sub>3</sub>)<sub>2</sub>
B
Na<sub>3</sub>PO<sub>4</sub>
C
Na<sub>6</sub>P<sub>6</sub>O<sub>18</sub>
D
Na<sub>2</sub>HPO<sub>4</sub>
Correct Answer: Na<sub>6</sub>P<sub>6</sub>O<sub>18</sub>