What role do calcium and magnesium play in the ion exchange process related to water softening?

In the context of water softening through ion exchange, calcium and magnesium are divalent cations responsible for water hardness. The primary role they play in this process is to be removed from the water.

During the ion exchange process, water passes through a resin bed that contains sodium ions. When hard water flows through this resin, the calcium and magnesium ions in the water are attracted to the negatively charged sites on the resin. As these hardness ions attach to the resin, sodium ions are released into the water in exchange. This process effectively reduces the concentration of calcium and magnesium in the treated water, resulting in "softer" water that is less likely to cause scale buildup in plumbing and appliances.

For the other options, adding calcium and magnesium would increase water hardness, filtering them out does not accurately describe the ion exchange mechanism, and chemically neutralizing them does not apply since their role is primarily in the removal process rather than any chemical alteration. Thus, the correct understanding of their role in water softening is that they are indeed removed from the water through the ion exchange process.