Which of the following agents is good for purifying drinking water? A. Catalytic agent B. Reducing agent C. Sterilizing agent D. Oxidizing agent

Drinking water is purified by killing the disease-causing germs in it, that is, by sterilising (disinfecting) it. Agents such as chlorine, bleaching powder and ozone are used for this. (They kill germs by oxidising them, which is why some keys also accept 'oxidizing agent', but the purpose they serve is sterilisation.)