Temporary hardness in water is caused by the presence of dissolved calcium and magnesium ions. These ions can combine with substances in the water to form insoluble precipitates, which can create hardness. The most common substances that calcium and magnesium ions combine with in water are hydrogencarbonates.
Option 1: Hydrogencarbonates - This is the correct answer. Calcium and magnesium hydrogencarbonates are formed when these ions react with dissolved carbon dioxide in water. These hydrogencarbonates contribute to temporary hardness in water.
Option 2: Carbonates - While calcium and magnesium can also combine with carbonates, it is the hydrogencarbonates that are primarily responsible for temporary hardness.
Option 3: Chlorides - Calcium and magnesium chlorides do not contribute significantly to temporary hardness in water.
Option 4: Sulphates - Similarly, calcium and magnesium sulphates do not play a major role in temporary hardness compared to hydrogencarbonates.
It is important to note that temporary hardness can be removed by boiling the water or adding lime (calcium hydroxide) to precipitate out the hydrogencarbonates.