What chemical element is commonly used to remove chlorine from water?

Sodium thiosulfate is widely recognized for its effectiveness in removing chlorine from water. This chemical acts as a reducing agent, which means it can react with chlorine and neutralize it, thereby rendering the chlorine harmless. When sodium thiosulfate is added to chlorinated water, it forms chloride ions and sulfate, effectively eliminating the residual chlorine that could be harmful to aquatic life or interfere with water treatment processes.

Understanding the different chemicals can help clarify their functions: chlorine is often used in water treatment for disinfection, but once the disinfection process is complete, any remaining chlorine must be removed to avoid negative impacts. Sodium thiosulfate is a reliable choice for this purpose due to its efficiency, safety profile, and ease of use in various treatment scenarios.

In contrast, the other options do not serve the same function. Nitrogen tetraoxide does not have a role in chlorine removal, and chloramine is actually a compound formed from chlorine and ammonia, which is sometimes used as a disinfectant itself. Calcium hydroxide, while useful in other aspects of water treatment such as pH adjustment, does not directly remove chlorine.