Why is chlorine often tested in water treatment?

Chlorine is commonly tested in water treatment primarily to evaluate disinfection effectiveness. In the context of water treatment, chlorine serves as a disinfectant that helps eliminate harmful pathogens, bacteria, and viruses that can pose health risks to humans. By measuring the concentration of chlorine in the water, treatment facilities can ensure that a sufficient level of disinfection is being achieved, thereby protecting public health.

Monitoring chlorine levels is crucial because it allows operators to adjust the dosage as needed, ensuring that the water is safe for consumption while considering factors such as the water's quality and the presence of contaminants. A proper level of chlorine will effectively reduce microbial populations without introducing excessive residual chlorine that could lead to taste or odor issues.

The other options are focused on different water quality parameters that do not directly relate to the primary functions of chlorine in water treatment. Hardness and alkalinity are measures of mineral content and buffering capacity, respectively, while acidity pertains to pH levels. None of these are the primary uses of chlorine in the treatment process. Thus, selecting the option related to disinfection effectiveness is aligned with its role in promoting safe drinking water through proper microbial control.