Which statement correctly describes temporary hardness and permanent hardness and how each is removed?

• A. Temporary hardness can be removed by boiling; permanent hardness can be removed by distillation.
• B. Temporary hardness can be removed by boiling; permanent hardness can be removed by ion exchange.
• C. Temporary hardness can be removed by ozonation; permanent hardness cannot be removed.
• D. Both types can be removed by filtration only.

Answer: (B)

The key idea is understanding what causes water hardness and how each type can be removed. Temporary hardness comes from dissolved bicarbonate salts of calcium and magnesium. When you boil the water, these bicarbonates break down into carbonate, carbon dioxide, and water, and the carbonate combines with calcium or magnesium to form insoluble calcium carbonate or magnesium carbonate that precipitates out. This is why boiling effectively removes temporary hardness.

Permanent hardness, on the other hand, is due to non-bicarbonate salts like sulfates and chlorides of calcium and magnesium. Boiling won’t remove these, because they don’t decompose or precipitate with heat. A common and effective method to remove them is ion exchange, where calcium and magnesium ions in the water are swapped with sodium ions on a resin, reducing hardness.

That’s why the statement pairing boiling as a remover for temporary hardness and ion exchange as a remover for permanent hardness is the best fit. Filtration alone can’t remove dissolved salts, and distillation or ozonation aren’t the standard approaches for addressing these specific hardness types.