Answer: Ion exchange method.
- A Ion exchange method
- B Boiling
- C Distillation of a small amount
- D Addition of Na2CO3
Correct answer: A. Ion exchange method
Explanation: Ion exchange resins replace Ca2+ and Mg2+ ions with Na+ (or H+), removing all types of hardness.
Each water molecule's O-H bonds (covalent, solid) can hydrogen-bond (dashed) to neighbouring molecules, forming an extended network responsible for water's unusually high boiling point and density anomaly.
Concept context
The simplest and most abundant element in the universe. Study its unique position in the periodic table, isotopes (protium, deuterium, tritium), properties of water and hydrogen peroxide, and industrial uses.