Final answer:
The Fontana-Masson stain is best for demonstrating melanin, as it uses a silver-based technique to make the pigment visible under a microscope. Option C.
Step-by-step explanation:
The method that best demonstrates melanin is C. Fontana-Masson stain. Among the provided options, Fontana-Masson is specifically designed to stain melanin granules. This stain is a silver-based technique where melanin granules reduce silver to a visible metallic silver, resulting in the granules being highlighted with a dark color.
This makes the pigment stand out in tissue sections for microscopic examination. The other options listed, such as Periodic acid-Schiff (PAS) stain, Masson's trichrome stain, and Oil Red O stain, are used for different staining purposes and would not be appropriate for specifically targeting melanin. Option C.