Which of the following compounds is used for water softening ?

Options

A. `Ca_3(PO_4)_2`
B. `Na_3PO_4`
C. `Na_6P_6O_(18)`
D. `Na_2HPO_4`

Answer

C

Explanation

For water softening, sodium hexametaphosphate is used. The chemical formula is
`Na_(2)[Na_(4)(PO)_(3)]_(6)=Na_(6)P_(6)O_(18).` The trade name is calgon.
`underset("water)") underset("(From hard ")(2CaCl_2)+underset("hexametaphosphate")underset("Sodium")(Na_2[Na_4(PO_3)_6])rarrunderset("Complex salt (soluble)")(Na_2[Ca_(2)(PO_3)_6])+4NaCl`