Which acid is more available when the pH is low?

When the pH of water is low, hypochlorous acid (HOCl) is more available and effective as a sanitizer. This is because hypochlorous acid forms from chlorine when it is dissolved in water, and its presence is highly dependent on the pH level. At lower pH levels, the balance tips in favor of hypochlorous acid as opposed to hypochlorite ion (OCl-), which dominates at higher pH levels.

Hypochlorous acid is the more potent form of chlorine for disinfection and sanitation purposes. It is able to penetrate microbial cell walls more effectively than its ionized counterpart, resulting in better antimicrobial efficacy. Conversely, other chlorine-based options, like chlorine dioxide and trichloroisocyanuric acid, do not exhibit the same relationship with pH in terms of increased availability. For instance, trichloroisocyanuric acid is a chlorine compound that typically dissociates to form hypochlorite ions more effectively at neutral and higher pH levels rather than at low pH, while calcium hypochlorite generally produces hypochlorite ions as well, with the same limitations related to pH.

Thus, among the listed answers,