Chlorine is widely used for ___.

• A. Filtration
• B. Sterilization
• C. Disinfection
• D. Flocculation

Answer: (C)

Disinfection is the process of inactivating disease-causing organisms, and chlorine is widely used because it reliably inactivates bacteria, viruses, and many parasites while leaving a protective residual in the water to prevent recontamination in the distribution system. Filtration and flocculation are physical/chemical steps that remove particles or clump them together, not the primary mechanism for killing microbes. Sterilization implies complete elimination of all microorganisms, which isn’t achieved by ordinary chlorine use in water treatment, making disinfection the best description of chlorine’s role.