Consider the following statements: Hard water is not suitable for I. drinking. II. washing clothes with soap. III. use in boilers. IV. irrigating crops. Which of these statements are correct?

Hard water contains high concentrations of dissolved minerals, primarily calcium and magnesium, which make it unsuitable for various purposes as explained below:

First, for drinking, while not necessarily a health risk in small amounts, hard water can lead to digestive issues over time and is often rejected due to its unpleasant taste and potential to cause kidney stones.

Second, for washing clothes, the minerals in hard water react with soap to form an insoluble curd or scum. This prevents the soap from lathering effectively, wastes cleaning agents, and leaves a gray deposits on fabrics.

Third, for use in boilers, heating hard water causes minerals to precipitate and form a hard layer called scale. This scale acts as an insulator, reducing heating efficiency, clogging pipes, and potentially leading to boiler explosions.

Fourth, for irrigating crops, the high salt and mineral content can increase soil alkalinity and lead to salt accumulation. This affects the osmotic balance of plants, making it harder for them to absorb water and nutrients, which ultimately reduces crop yield.

Since hard water is unsuitable for all four activities mentioned, option D is the correct answer.