Which of the following methods cannot be used to remove permanent hardness in water?
A. Addition of washing soda B. Addition of caustic soda C. Permutit method D. Adding alum to water
Correct Answer: D
Explanation
Permanent hardness in water can be removed by ____________ (i) the use of permutit (ii) distillation (iii) the addition of calculated amount of \(\mathrm{NaOH}\) (caustic soda) (iv) the addition of \(\mathrm{Na}_2 \mathrm{CO}_3\) (washing soda) Temporary hardness can be removed by: (i) boiling (ii) distillation (iii) permutit (iv) adding \(\mathrm{Ca}(\mathrm{OH})_2\) (v) adding \(\mathrm{Na}_2 \mathrm{CO}_3\)