Which of the following is a correct pairing of a stain with its reagents?

• A. Gridley: Chronic acid and Metanil Yellow
• B. Grocott: Chronic and Periodic acid
• C. Gridley: Gram iodine and Crystal Violet
• D. Grocott: Ziehl-Neelsen reagents

Answer: (A)

Gridley staining uses an oxidative step with chromic acid followed by Metanil Yellow as a counterstain. This exact pairing is what defines the Gridley protocol, so matching chromic acid with Metanil Yellow is correct. The other options pair stains with reagents from different methods: Grocott’s methenamine silver involves silver impregnation after oxidation (not periodic acid), Gram staining relies on Crystal Violet and Gram iodine, and Ziehl-Neelsen uses carbol fuchsin with acid-alcohol decolorization and a counterstain.