**Core Concept**
Oil Red O staining is a lipophilic dye used to identify and visualize lipid-containing cells and structures in histological preparations. This staining technique is particularly useful in the diagnosis of various conditions, including lipid storage diseases and certain types of cancer.

**Why the Correct Answer is Right**
Oil Red O works by selectively staining triglycerides, cholesterol esters, and other lipids, making them visible under a microscope. This is achieved through the interaction of the dye with the lipid molecules, which leads to a color change, typically from red to pink, depending on the concentration of the dye and the type of lipid present. The staining is reversible, meaning that the lipids can be extracted with organic solvents, such as ethanol or acetone, without affecting the underlying tissue structure.

**Why Each Wrong Option is Incorrect**
**Option A:** Oil Red O staining is not typically used to identify glycogen-containing cells, as glycogen is a polysaccharide that is stained by other dyes, such as Periodic Acid-Schiff (PAS).
**Option B:** Oil Red O staining is not used to identify proteins, as it is a lipophilic dye that targets lipids, not proteins.
**Option C:** Oil Red O staining is not used to identify nucleic acids, as it is a lipophilic dye that targets lipids, not nucleic acids.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Oil Red O staining can be used in conjunction with other staining techniques, such as hematoxylin and eosin (H&E), to obtain a more comprehensive understanding of tissue morphology and lipid distribution.

**Correct Answer: C. Identifying lipid-containing cells.**