Correct Answer - C
Polyphosphates are used as water softening agents because they form soluble complexes with cationsresponsible for the hardness of water.
`2CaSO_(4)+Na_(2)[Na_(4)(PO_(3))_(6)]toNa_(2)[Ca_(2)(PO_(3))_(6)]+2Na_(2)SO_(4)`
`2MgSO_(4)+Na_(2)[Na_(4)(PO_(3))_(6)]toNa_(2)[Mg_(2)(PO_(3))_(6)]+2Na_(2)SO_(4)`