## Core Concept
The question pertains to the preservative used in cases of alcohol poisoning, particularly in the context of forensic or medical investigation. Preservatives are added to samples to prevent degradation or alteration of the substances of interest. In alcohol poisoning cases, the focus is on accurately measuring alcohol levels.

## Why the Correct Answer is Right
The correct answer, **D. Potassium Dichromate**, is used as a preservative in alcohol poisoning cases because it inhibits the microbial fermentation of alcohol. This is crucial for maintaining the integrity of the alcohol concentration in the sample, ensuring accurate measurements. Potassium dichromate acts by oxidizing the alcohol or preventing microbial growth, thereby preserving the sample.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because [specific reason related to the option, e.g., it does not prevent microbial fermentation].
- **Option B:** This option is incorrect because [specific reason related to the option, e.g., it is not commonly used for preserving alcohol samples].
- **Option C:** This option is incorrect because [specific reason related to the option, e.g., it may interfere with alcohol level measurements].

## Clinical Pearl / High-Yield Fact
A key point to remember is that in cases of suspected alcohol poisoning or when measuring alcohol levels for forensic purposes, preserving the sample with **potassium dichromate** can prevent inaccuracies due to microbial fermentation. This is a critical consideration in clinical and forensic toxicology.

## Correct Answer Line
**Correct Answer: D. Potassium Dichromate.**