__ is used to disinfect water sources A. phenolic compounds B. Sodium hypochlorite C. Etidium bromide D. Chlorine

The correct answer is D. Chlorine.<br /><br />Chlorine is commonly used to disinfect water sources. It is a powerful oxidizing agent that can effectively kill a wide range of microorganisms, including bacteria, viruses, and protozoa. Chlorine is added to water in the form of sodium hypochlorite or chlorine gas, which then reacts with the water to form hypochlorous acid. This acid is the active disinfectant that kills the microorganisms.<br /><br />Phenolic compounds (option A) are not typically used for water disinfection. They are organic compounds that are commonly used as disinfectants, but they are not as effective as chlorine for water treatment.<br /><br />Etidium bromide (option C) is a DNA intercalating agent that is used as a staining agent in molecular biology, not for water disinfection.<br /><br />Sodium hypochlorite (option B) is the chemical form of chlorine that is commonly used for water disinfection. It is a solution of chlorine in water and is the active ingredient in many household bleach products.