Which will produce hard water ?

Options

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

Answer

A

Explanation

`Ca^(2+)` and `Mg^(2+)` ions are responsible for hardness. Also `CaSO_4` is soluble in water to an appreciable amount.