question_answer 56)

  Which of the following compounds is used for water softening? (a)\[C{{a}_{3}}{{(P{{O}_{4}})}_{2}}\]                        (b) \[N{{a}_{3}}P{{O}_{4}}\]                        (c)\[N{{a}_{5}}{{P}_{6}}{{O}_{18}}\]                        (d)\[N{{a}_{2}}HP{{O}_{4}}\]

Answer:

  (c)\[N{{a}_{6}}{{P}_{6}}{{O}_{18}}\]or\[N{{a}_{2}}[N{{a}_{4}}{{(P{{O}_{3}})}_{6}}]\] is known as calgon. Calcium and magnesium salts present in hard water react with calgon to form complex salts.