As the temperature increases, the effectiveness of chlorine ___.

• A. Decreases
• B. Becomes unpredictable
• C. Increases
• D. Stays the same

Answer: (C)

Increasing temperature speeds up chemical reactions, so chlorine becomes more effective as a disinfectant. Higher temperature accelerates the reaction rates between chlorine species (mainly hypochlorous acid, HOCl, which is the more active form) and microbial components, and it also helps chlorine molecules diffuse faster through water to reach organisms. Because of these kinetic enhancements, disinfection efficiency improves with temperature. The other options don’t fit since disinfection kinetics generally do not become less predictable or stay the same across typical temp ranges, and they certainly don’t decrease just because it’s warmer.