Which one of the following processes will produce hard water?

Options

A. Saturation of water with `CaCO_3`
B. Saturation of water with `MgCO_3`
C. Saturation of water with `CaSO_4`
D. Addition of `Na_2SO_4`, to water

Answer

C

Explanation

Alkaline earth metal salts cause hardness. Temporary hardness is caused by soluble Ca and Mg hydrogen carbonates. Soluble sulphates and chlorides of calcium and magnesium cause permanent hardness.