Which of the following chemicals is used to measure water quality?

Chlorine is widely recognized as a chemical used to measure and manage water quality. It serves essential roles in water treatment processes, particularly as a disinfectant. By adding chlorine to water, it effectively eliminates pathogens such as bacteria, viruses, and protozoa, thereby ensuring the safety of drinking water. Monitoring chlorine levels in water can also provide insights into the effectiveness of disinfection efforts and the overall microbiological quality of the water supply.

In addition to its disinfectant properties, chlorine is often measured in water quality assessments to evaluate the degree of chlorine residual present, which indicates ongoing disinfection capability. Adequate levels of chlorine are critical to prevent waterborne diseases and to ensure that the treated water remains safe until it reaches consumers.

Other chemicals listed, such as fluoride, bromine, and aluminum, have specific roles in water treatment but are not primarily used as indicators of overall water quality. Fluoride is usually added for dental health benefits, bromine is a disinfectant mainly for pools, and aluminum may be used in some coagulation processes in water treatment but does not measure water quality directly.