**Core Concept**
The Fontana-Masson stain is a histological technique used to identify and visualize melanin-containing cells and structures in tissue sections. This stain is particularly useful for diagnosing conditions related to melanin production, such as melanoma.

**Why the Correct Answer is Right**
The Fontana-Masson stain reacts with the indole nucleus of melanin, resulting in a brown-black precipitate that is visible under the microscope. This stain is specific for melanin-containing cells, including melanocytes, melanophages, and melanoma cells. The stain works by reacting with the indole nucleus of melanin, which is then visualized as a dark brown-black precipitate.

**Why Each Wrong Option is Incorrect**
**Option A:** The Alcian blue stain is used to identify mucopolysaccharides, not melanin.
**Option B:** The Prussian blue stain is used to identify iron deposits, not melanin.
**Option C:** The Periodic acid-Schiff (PAS) stain is used to identify glycogen and other carbohydrates, not melanin.

**Clinical Pearl / High-Yield Fact**
The Fontana-Masson stain is a valuable tool in the diagnosis of melanoma, particularly in cases where the diagnosis is uncertain. It is essential to note that the Fontana-Masson stain is not specific for melanoma, and other conditions that produce melanin, such as pigmented Bowen's disease, can also stain positive.

**Correct Answer:** C. Melanin granules