Hardness of water is due to the presence of salts of -

Correct option is C

Sol. Hardness of water is caused by dissolved salts of calcium (Ca²⁺) and magnesium (Mg²⁺), which react with soap to form scum and cause scale buildup in pipes and appliances. Temporary hardness is due to bicarbonates, while permanent hardness is caused by sulfates and chlorides.
Explanation of Each Option:
· Chlorine: Incorrect; used to disinfect water, but does not cause hardness.
· Boron: Incorrect; a trace element in water, but not responsible for hardness.
· Magnesium: Correct answer; along with calcium, it contributes to water hardness.
· Potassium: Incorrect; a necessary electrolyte in water, but does not cause hardness.