## Core Concept
The question tests the understanding of how to handle water samples for bacteriological analysis that may contain disinfectants like chlorine. Chlorine is a strong disinfectant that can kill bacteria, thereby affecting the results of bacteriological water analysis.

## Why the Correct Answer is Right
The correct answer, **Sodium thiosulphate**, is used to neutralize chlorine in water samples. Chlorine can be present in water as a disinfectant and can interfere with bacteriological analysis by killing the bacteria being cultured. Sodium thiosulphate reacts with chlorine to form harmless products, thereby neutralizing its effect. This allows for the accurate culture of bacteria present in the water sample.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not specify a substance known to neutralize chlorine.
- **Option B:** This option is incorrect as there is no common substance used for neutralizing chlorine in water samples that is widely recognized by this description.
- **Option C:** This option might seem plausible but is not the correct answer because **Sodium thiosulphate** is specifically known for its use in neutralizing chlorine.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when dealing with water samples that may contain disinfectants like chlorine for bacteriological analysis, adding **Sodium thiosulphate** can help neutralize the chlorine. This ensures that the bacteria present in the sample are not killed before they can be cultured, providing an accurate representation of the microbial content of the water.

## Correct Answer: D. Sodium thiosulphate.