**Core Concept**
Fats are lipids that can be stained using specific dyes due to their chemical properties. In histopathology, various stains are used to differentiate between different tissue components, including lipids.

**Why the Correct Answer is Right**
The correct answer is Sudan III, a lipophilic dye that selectively stains lipids in tissue sections. Sudan III works by dissolving in the lipid droplets, causing them to appear stained under a microscope. This is due to the lipophilic nature of Sudan III, which allows it to penetrate and bind to the lipids in the tissue.

**Why Each Wrong Option is Incorrect**
* **Option A:** The correct answer is not Hematoxylin, as it is a basic dye used for staining nuclei and does not selectively stain lipids.
* **Option B:** The correct answer is not Methylene Blue, as it is an acidic dye used for staining bacteria and does not selectively stain lipids.
* **Option C:** The correct answer is not Alizarin Red, as it is a metachromatic dye used for staining calcium deposits and does not selectively stain lipids.

**Clinical Pearl / High-Yield Fact**
Sudan III is a classic histopathological stain used to detect lipids in tissue sections. When using Sudan III, it's essential to use a fixative that preserves the lipids, such as formalin, to ensure accurate staining.

**Correct Answer: D. Sudan III**