A trihydric alcohol in chemistry is defined by the presence of three hydroxyl (-OH) groups. The following analysis identifies the trihydric alcohol among the given options:
- Ethanol (C2H5OH): This compound possesses a single hydroxyl group, thus it is a monohydric alcohol.
- Glycerol (C3H5(OH)3): With three hydroxyl groups, Glycerol is classified as a trihydric alcohol.
- Ethylene Glycol (C2H4(OH)2): This substance has two hydroxyl groups, categorizing it as a dihydric alcohol.
- Phenol (C6H5OH): Phenol contains one hydroxyl group, classifying it as a monohydric alcohol.
Glycerol is identified as the correct answer due to its molecular structure, which features three hydroxyl groups, uniquely among the provided options.