Which factor has the least effect on the rate of chlorine reaction with microorganisms?

The presence of sunlight has the least effect on the rate of chlorine reaction with microorganisms compared to the other factors listed.

Chlorination is primarily a chemical reaction involving chlorine and microorganisms. The effectiveness and speed of this reaction can be influenced by the concentration of chlorine, as higher concentrations typically boost the reaction rate. The type of microorganisms also plays a significant role since different types respond to chlorination at varying rates; for instance, bacteria may be more susceptible to chlorine than certain protozoa. Additionally, the temperature of the water affects the kinetic energy of molecules, which in turn influences how quickly chlorine can react with microorganisms—generally, higher temperatures promote faster reactions.

While sunlight can lead to the degradation of chlorine in water, it is not a direct influencer of chlorine's effectiveness against microorganisms. Thus, it has a relatively minor role compared to the biochemical aspects of temperature, concentration, and the diversity of microorganisms present.