Counterstain used in PAS.

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Multiple Choice

Counterstain used in PAS.

Explanation:
In PAS, the magenta color marks carbohydrates after the Schiff reaction, so the counterstain is chosen to provide clear contrast and reveal tissue architecture. Aluminum hematoxylin is the common nuclear counterstain because it gives a crisp, durable blue nuclei that stays distinct after PAS processing. Pairing it with a light green counterstain adds contrast to the cytoplasm and background without overpowering the magenta, making it easier to differentiate cellular components and tissue structures. This combination—aluminum hematoxylin for nuclei with a light green counterstain for the rest of the tissue—is typical for producing a clean, interpretable PAS slide. Eosin would clash with the magenta, and Azure II or methylene blue aren’t standard choices for this staining sequence.

In PAS, the magenta color marks carbohydrates after the Schiff reaction, so the counterstain is chosen to provide clear contrast and reveal tissue architecture. Aluminum hematoxylin is the common nuclear counterstain because it gives a crisp, durable blue nuclei that stays distinct after PAS processing. Pairing it with a light green counterstain adds contrast to the cytoplasm and background without overpowering the magenta, making it easier to differentiate cellular components and tissue structures. This combination—aluminum hematoxylin for nuclei with a light green counterstain for the rest of the tissue—is typical for producing a clean, interpretable PAS slide. Eosin would clash with the magenta, and Azure II or methylene blue aren’t standard choices for this staining sequence.

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