Multiple choice Which of the following is used for softening hard water? (NaPO3)6 Ca(NO3)2.NH4NO3 Ca(H2PO4)2.+CaSO4.2H2O KNO3 None of these Reveal answer Fill a bubble to check yourself A Correct answer Explanation This option is correct because sodium hexametaphosphate is a polymeric salt of metaphosphoric acid. It is used for softening hard water under the trade name calgon.