Permanent hardness in water is due to the presence of the chlorides, nitrates and sulphates of calcium and magnesium. It is not precipitated by boiling. These minerals in water can cause some everyday problems. Hard water may also shorten the life of plumbing and water heaters. The lime scale can build up on the inside of the pipe restricting the flow of water or causing a blockage.

so the correct answer is D) Calcium sulphate

The permanent hardness of water is due to the presence of calcium bicarbonate and magnesium bicarbonate.

Explanation:

The term "hard water" refers to water that contains high levels of dissolved minerals, particularly calcium and magnesium ions. These minerals are usually present in the form of bicarbonates, sulfates, or chlorides.

The hardness of water can be classified into two types - temporary and permanent hardness. Temporary hardness is caused by the presence of dissolved bicarbonate ions, which can be removed by boiling the water or adding lime (calcium hydroxide) to precipitate the calcium and magnesium ions. On the other hand, permanent hardness cannot be removed by boiling and is caused by dissolved sulfates and chlorides of calcium and magnesium.

The permanent hardness of water is primarily due to the presence of calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2). When water containing these bicarbonates is heated or left to stand, it undergoes a chemical reaction called thermal decomposition or hydrolysis. This reaction leads to the formation of insoluble calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitates, which contribute to the hardness of water.

The reaction can be represented as follows:
Ca(HCO3)2 + heat → CaCO3 + CO2 + H2O
Mg(HCO3)2 + heat → MgCO3 + CO2 + H2O

The calcium carbonate and magnesium carbonate precipitates are responsible for the formation of scale or deposits on household appliances and plumbing systems. These deposits can reduce the efficiency of water heaters, clog pipes, and affect the performance of washing machines, dishwashers, and other water-based appliances.

In summary, the permanent hardness of water is caused by the presence of calcium bicarbonate and magnesium bicarbonate, which undergo hydrolysis upon heating or standing to form insoluble calcium carbonate and magnesium carbonate precipitates.