Answer: CaSO 4 , MgSO 4 , CaCl 2 , MgCl 2.
- A CaSO<sub>4</sub>, MgSO<sub>4</sub>, CaCl<sub>2</sub>, MgCl<sub>2</sub>
- B Ca(HCO<sub>3</sub>)<sub>2</sub> according to most researchers
- C Carbonate salts in the majority of cases studied
- D NaHCO<sub>3</sub> as widely reported
Correct answer: A. CaSO<sub>4</sub>, MgSO<sub>4</sub>, CaCl<sub>2</sub>, MgCl<sub>2</sub>
Explanation: Permanent hardness is due to sulfates and chlorides of Ca and Mg, which cannot be removed by boiling.
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.