Discard Schiff reagent when solution turns.

• A. Clear
• B. Pink
• C. Brown
• D. Yellow

Answer: (B)

Schiff reagent is used in PAS staining to reveal aldehydes formed after oxidation of carbohydrates; fresh reagent is colorless, and it develops a magenta color when aldehydes are present. If the reagent has aged or been exposed to air, it loses its reducing ability and will turn pink, signaling that it’s oxidized and no longer reliable for proper staining. Discarding it at the first pink change helps ensure accurate, specific results with minimal background. Clear, brown, or yellow do not consistently indicate readiness for discard in the same way pink does, so pink is the standard cue to replace the reagent.