This substance is described as highly sensitive for lipid but not permanent in tissue sections:

• A. 3,4-Benzpyrene
• B. Oil Red O
• C. Nile Blue Sulfate
• D. OTAN

Answer: (A)

The main idea here is about a dye that targets lipids but isn’t preserved through routine tissue processing. Oil Red O is the classic example. It binds strongly to neutral lipids, giving a vivid red stain for fats like triglycerides and cholesterol esters. Yet lipids are removed during the dehydration and clearing steps of paraffin embedding, so the stain doesn’t remain in the section once standard processing is complete. To keep the lipid staining, you use frozen tissue sections and aqueous mounting, which preserves both the lipids and the stain.

Other choices don’t fit this description. A polycyclic aromatic hydrocarbon like 3,4-Benzpyrene isn’t a lipid stain at all; it’s a carcinogen. Nile Blue Sulfate and OTAN are different dyes with other targets, and they don’t exemplify the highly lipid-specific, non-permanent staining behavior that Oil Red O shows.