What is the reason for the hardness of water?
Answer & explanation
Correct answer: option 3
The correct answer is option 3. Ca2+ and Mg2+.
The hardness of water is primarily caused by the presence of calcium ions (Ca²⁺) and magnesium ions (Mg²⁺). These ions are dissolved in water and can form insoluble compounds, such as carbonates and sulfates, which contribute to the hardness.
So, the correct answer is: Ca²+ and Mg²+