What chemical is present in a bacteria sample bottle for the purpose of neutralizing chlorine?

Sodium thiosulfate is the correct choice for neutralizing chlorine in a bacteria sample bottle. It serves as a dechlorinating agent due to its ability to react with chlorine, effectively reducing its toxicity and allowing for accurate testing of microbial content. When sodium thiosulfate is added to a sample containing chlorine, it reacts to form non-toxic products, which is essential for procedures in microbiological testing where chlorine can kill bacteria and lead to inaccurate results.

Other substances listed do not effectively serve this purpose. Activated carbon can remove chlorine through adsorption, but it isn’t a chemical neutralization process. Hydrochloric acid would actually increase acidity and could interfere with tests by altering environmental conditions. Calcium carbonate might influence the pH but does not neutralize chlorine effectively. Thus, sodium thiosulfate is uniquely suited for this role in preparing samples for analysis.