Final answer:
Chlorine is a reactive nonmetal gas that acts as a powerful disinfectant for pools and municipal water treatment. It is commonly used in the form of hypochlorous acid to kill bacteria and other microbes in drinking water supplies and swimming pools.
Step-by-step explanation:
The reactive nonmetal that is a gas and a powerful disinfectant for pools and municipal water treatment is chlorine. Chlorine is commonly used in the form of hypochlorous acid to kill bacteria and other microbes in drinking water supplies and public swimming pools. In most private swimming pools, sodium hypochlorite or solid tablets of chlorinated isocyanurates are used instead of chlorine itself.