Which among the following is a trihydric alcohol?

Glycerol

The correct answer is Option (2) → Glycerol

Let's break down each compound to understand why glycerol is the trihydric alcohol among the options:

1. Ethanol 

Ethanol contains only one hydroxyl group (-OH) attached to an ethyl group \((C_2H_5)\). This is a monohydric alcohol, meaning it has only one hydroxyl group.

2. Glycerol

Glycerol has three hydroxyl groups (-OH), each attached to a carbon atom in a chain of three carbon atoms. This makes it a trihydric alcohol, meaning it has three hydroxyl groups. Each of these hydroxyl groups is capable of forming hydrogen bonds, which makes glycerol highly hydrophilic (water-attracting).

Each carbon atom is attached to a hydroxyl group, making glycerol a trihydric alcohol.

3. Ethylene Glycol

Ethylene glycol contains two hydroxyl groups (-OH), one attached to each of the two carbon atoms in a chain. This is a dihydric alcohol, meaning it has two hydroxyl groups.

4. Phenol

Phenol is not classified as an alcohol in the strict sense because it has a hydroxyl group (-OH) directly attached to a benzene ring, which makes its chemistry different from typical alcohols. Phenol is considered an aromatic compound with a hydroxyl group but not a typical alcohol.

This compound has only one hydroxyl group.

Summary

Glycerol is a trihydric alcohol because it has three hydroxyl (-OH) groups. Ethanol and ethylene glycol have fewer hydroxyl groups (1 and 2, respectively), and phenol is an aromatic compound, not an alcohol.

Thus, glycerol is the correct answer.