In Mayer's Mucicarmine staining, which chemical forms a chelation complex with carmine to give a net positive charge for attachment to mucin?

• A. Aluminum forms a chelation complex with carmine
• B. Iron forms a complex
• C. Calcium forms a complex
• D. Magnesium forms a complex

Answer: (A)

The key idea is that the dye needs a positively charged complex to bind to mucin, which carries negative charges. In Mayer's mucicarmine, aluminum acts as the mordant by forming a chelation complex with carmine. This aluminum–carmine complex has a net positive charge, allowing it to electrostatically attach to the negatively charged mucin in the tissue, giving mucin its characteristic magenta stain. Other metals like iron, calcium, or magnesium don’t form the same positively charged complex with carmine in this method, so they don’t provide the same mucin binding.