**Core Concept**
The assessment of alcohol in expired air involves the use of a chemical that reacts with alcohol to produce a detectable change, allowing for qualitative and quantitative evaluation. This process relies on the principle of chemical reactivity and specificity.

**Why the Correct Answer is Right**
The chemical used for this purpose is often **Silica Gel Impregnated with Chromium (III) Oxide**. When alcohol is present in the expired air, it reacts with the chromium (III) oxide to produce a color change, indicating the presence of alcohol. This reaction is specific to alcohol and does not occur with other substances, making it a reliable method for assessment.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a commonly used chemical for alcohol assessment.
* **Option B:** This is not a specific chemical that reacts with alcohol to produce a detectable change.
* **Option C:** This is not a chemical used for alcohol assessment in expired air.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the chemical used for alcohol assessment in expired air is specific to chromium (III) oxide, and other substances may not produce a similar reaction. This specificity is crucial for accurate qualitative and quantitative assessment of alcohol.

**Correct Answer: B. Silica Gel Impregnated with Chromium (III) Oxide**