Final answer:
The correct answer is (c) Yes, any acidic dye can be used as a negative stain, as these dyes are repelled by the negatively charged cell walls, unlike basic dyes that stick to the cell walls.
Step-by-step explanation:
The question is asking whether any dye could be substituted for nigrosin in a negative staining procedure. The correct answer is (c) Yes, any acidic dye can be used. Acidic dyes have negatively charged chromophores which are repelled by the negatively charged cell walls, making them suitable for negative staining. In contrast, basic dyes like crystal violet and methylene blue, which have positively charged chromophores, are attracted to the cell walls and are used as positive stains. Therefore, in addition to nigrosin, other acidic dyes such as India ink, acid fuchsin, eosin, and rose bengal can also be used for negative staining.