Which of the following types of hardness is considered temporary?

Temporary hardness in water primarily refers to hardness that can be removed by boiling. This type of hardness is mainly caused by the presence of dissolved bicarbonate minerals, such as calcium bicarbonate and magnesium bicarbonate. When water containing these bicarbonates is heated, the bicarbonates decompose into carbonates, which precipitate out of solution as insoluble carbonates, such as calcium carbonate. This process effectively reduces the concentration of hardness-causing minerals in the water.

The correct answer, therefore, highlights the significance of carbonate hardness as it is directly linked to the presence of bicarbonate ions that can be eliminated through boiling. In contrast, non-carbonate hardness, caused by sulfates and chlorides, does not diminish with boiling. Similarly, organic hardness and salt hardness are associated with other compounds that do not fit the criteria for temporary hardness.