Discussion
The hardness in water is typically caused by the presence of :
Answer: D
Hardness is caused by calcium and magnesium ions.
Hard water contains dissolved Ca2+ and Mg2+ picked up from limestone, dolomite and gypsum. These ions react with soap to form scum instead of lather, and when the water is heated they precipitate as scale. Hardness is expressed as mg/L of CaCO3.
Carbonate and bicarbonate ions are the anions that make part of the hardness 'temporary' (removable by boiling), but the hardness itself is due to the cations. Sodium and potassium are monovalent and do not cause hardness. Suspended matter causes turbidity, not hardness.
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