After chlorination, what does the free chlorine residual include?

The free chlorine residual is a crucial measure in water treatment that indicates the amount of available chlorine left in the water after chlorination. This available chlorine is primarily in the forms of hypochlorous acid (HClO) and hypochlorite ion (OCl-). Both of these species play a significant role in disinfection, as they are the active forms of chlorine that can effectively kill pathogens.

When chlorine is added to water, it reacts to form hypochlorous acid and hypochlorite ion, which together comprise the total free chlorine residual. This residual is important for ensuring that adequate disinfection occurs and is typically monitored to ensure water quality standards are met.

Other choices presented do not consist of free chlorine residual. For instance, hydrogen peroxide is not a chlorine compound and does not contribute to chlorine residual. Chloramine, while a disinfectant, is a combined form of chlorine and ammonia, not free chlorine. Ozone is a different type of disinfectant altogether and does not contribute to chlorine residual. Sodium hypochlorite is a chlorine compound used for disinfection, but when it is added to water, it dissociates into free chlorine, which is measured as hypochlorous acid and hypochlorite ion