Option 1: Treatment with washing soda: This method involves adding washing soda (sodium carbonate) to hard water. Washing soda reacts with the calcium and magnesium ions, forming insoluble precipitates that can be filtered out. Therefore, this method can effectively remove permanent hardness from water.

Option 2: Calgon`s method: Calgon is a brand of water softener that contains sodium hexametaphosphate. When added to hard water, it forms complexes with calcium and magnesium ions, preventing them from forming insoluble precipitates and keeping them in solution. This method is specifically designed for removing permanent hardness from water, making it an effective solution.

Option 3: Boiling: Boiling water can help remove temporary hardness caused by the presence of bicarbonate ions that decompose into carbonate ions upon heating. However, boiling does not remove permanent hardness, as it is caused by the presence of dissolved calcium and magnesium sulfates or chlorides which do not dissociate upon heating. Therefore, this method is not effective for removing permanent hardness.

Option 4: Ion exchange method: Ion exchange involves passing hard water through a resin bed containing sodium ions. The calcium and magnesium ions in the water are exchanged with the sodium ions on the resin, effectively removing the hardness. This method