A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory, there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard.(A) Sodium chloride, Potassium chloride(B) Sodium sulphate, Potassium sulphate(C) Sodium sulphate, Calcium sulphate(D) Calcium sulphate, Calcium chloride

Correct Answer: (D) Calcium sulphate, Calcium chloride.

Explanation: Hard water can be prepared by dissolving sulphates, chlorides or bicarbonate salts of Ca²⁺ or Mg²⁺ ions.