Discussion
Permanent hardness of water is caused due to :
Answer: A
Permanent hardness is caused by magnesium sulphate.
Hardness comes from dissolved calcium and magnesium salts. Permanent (non-carbonate) hardness is due to their sulphates and chlorides, such as magnesium sulphate, which do not precipitate on boiling and must be removed by ion exchange or lime-soda treatment.
Bicarbonates of calcium and magnesium cause temporary hardness, which boiling removes by precipitating the carbonates. Magnesium carbonate itself is barely soluble, and sodium chloride does not cause hardness at all, since sodium ions do not form scum with soap.
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