Question

Which of the following is the hard water?

• A. Sea water
• B. Rain water
• C. Distilled water
• D. Demineralised water

Answer 1

The correct option is A Sea water

Sea water is the hard water because it has several dissolved salts. Mainly salts of calcium and magnesium gives hardness to the water. Hard water doesn't produce lather with soap solution readily because the salts react with soap solution and precipitates. Since, sea water doesn't form lather with soap solution, it is a hard water.
Whereas, in rain water, distilled water and demineralised water there won't be any dissolve salt of calcium and magnesium. Hence, they won't get precipitated so they form lather with soap solution. These are called soft water.