Answer:
Chlorine
Step-by-step explanation:
Chlorine is a halogen that is a strong oxidizer (it takes electrons from nearby compounds). In so doing, it kills bacteria, viruses, and other microorganisms. The chlorine reacts with cell walls or other vital organic compounds (e.g., proteins) to render them useless. Chlorine is relatively inexpensive and generally easy to handle, but it is dangerous in gaseous form and highly alkaline in solution, so must be stored and handled properly.