## **Core Concept**
The question tests the knowledge of histological staining techniques, specifically for identifying acid mucins. Acid mucins are a type of mucopolysaccharide found in connective tissue, and their detection is crucial in the diagnosis of various pathological conditions.

## **Why the Correct Answer is Right**
The correct answer, **Alcian Blue**, is a specific stain used to demonstrate acid mucins. Alcian Blue is a cationic dye that binds to the negatively charged sulfate and carboxyl groups of acid mucins, making them visible under a microscope. This stain is particularly useful in distinguishing acid mucins from neutral mucins, which are stained by Periodic Acid-Schiff (PAS).

## **Why Each Wrong Option is Incorrect**
* **Option A:** PAS (Periodic Acid-Schiff) is used to stain neutral mucins, glycogen, and glycoproteins, not acid mucins.
* **Option B:** Mucicarmine is a stain used to identify mucins, but it is not specific for acid mucins.
* **Option D:** Hematoxylin and Eosin (H&E) is a general-purpose stain, but it is not specific for acid mucins.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Alcian Blue stain is often used in conjunction with PAS to differentiate between acid and neutral mucins. This is particularly important in the diagnosis of certain tumors, such as adenocarcinomas.

## **Correct Answer:** . Alcian Blue