Which chemical compounds are part of the "exchange" stage in a softener's regeneration cycle?

The regeneration cycle of a water softener involves the exchange of ions, where calcium (Ca²⁺) and magnesium (Mg²⁺) ions in hard water are replaced by sodium (Na⁺) ions from the salt used in the softening process. The correct choice mentions several compounds, which accurately reflects the components of this ion exchange process.

In a well-functioning softener, the presence of compounds like CaHCO3 and MgHCO3 is significant because they represent the forms of calcium and magnesium found in hard water. During regeneration, the ion-exchange resin is flushed with a brine solution, typically containing NaCl. This regeneration is essential for the softener to continue its function effectively.

The inclusion of other salts, such as MgSO4 and CaSO4, in the correct option indicates the broader spectrum of compounds that may participate in the exchange process. In this context, these compounds are relevant as they also contain calcium and magnesium, which can be exchanged for sodium ions. Thus, the presence of multiple compounds in the correct answer represents the complexity of hard water chemistry and the effectiveness of the softening process.