(A) Treatment with washing soda is treatment with Na2CO3. (B) Calgon is Na6P6O18. It is used to soft the hard water. (C) Clark's method is used for lime softening i.e. Ca(OH)2 (D) Zeolite\/permutit process is a modern technique used to soften the hard water hydrated 'sodium aluminium silicate' i.e. (NaAlSiO4) is called permutit. Thus, option (b) is the correct answer. i.e.,