What substance can neutralize hydrochloric acid produced from chlorine gas disinfectants?

Caustic soda, also known as sodium hydroxide, is an effective neutralizing agent for hydrochloric acid. When caustic soda is added to hydrochloric acid, a neutralization reaction occurs, producing water and sodium chloride (table salt) as byproducts. This reaction helps to raise the pH level, effectively counteracting the acidity of hydrochloric acid.

In the context of pool chemistry, chlorine gas can produce hydrochloric acid during some disinfection processes. Therefore, having a method for neutralizing this acid is essential for maintaining balanced water chemistry and ensuring safe conditions in a swimming pool environment.

The other substances mentioned do not effectively neutralize hydrochloric acid. Bleach is primarily a disinfectant and can actually produce harmful gases when mixed with acids. Vinegar, being an acetic acid, would not neutralize hydrochloric acid and would only contribute to the acidity. Ammonia can react with acids but does not effectively neutralize hydrochloric acid, and its reaction can also potentially create toxic fumes. Thus, caustic soda stands out as the correct choice for neutralizing hydrochloric acid.