Hard water contains which of the following salts?
- ACalcium and sodium
- BMagnesium and calcium
- CBarium and calcium
- DCalcium and potassium
Show answer and explanation
Correct answer: (b) Magnesium and calcium
Explanation
Hard water contains dissolved salts of calcium and magnesium: their bicarbonates (temporary hardness, removed by boiling) and their chlorides and sulphates (permanent hardness).
These ions form a scum with soap instead of a lather, and they leave scale in kettles and boilers. Sodium and potassium salts do not make water hard, and barium is not normally present in water.