Diethylene glycol is obtained by heating glycol with:

Options

A. Conc. `H_(2)SO_(4)`
B. Conc. `H_(3)PO_(4)`
C. Aq. KOH
D. Conc. `HNO_(3)`

Explanation

To solve the question regarding the formation of diethylene glycol from glycol, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Structure of Glycol**:
Glycol, also known as ethylene glycol, has the chemical formula C2H6O2 and its structure can be represented as HO-CH2-CH2-OH. It contains two hydroxyl (–OH) groups.

2. **Understand the Reaction Conditions**:
We need to determine which reagent, when heated with glycol, will lead to the formation of diethylene glycol. The options given are concentrated H2SO4, concentrated H3PO4, aqueous KOH, and concentrated H2SO4.

3. **Analyze the Role of Concentrated H2SO4**:
When glycol is heated with concentrated sulfuric acid (H2SO4), both hydroxyl groups can be protonated. This leads to the formation of dioxane, which is not diethylene glycol.

4. **Analyze the Role of Concentrated H3PO4**:
When glycol is heated with concentrated phosphoric acid (H3PO4), only one of the hydroxyl groups gets protonated. This allows for the formation of diethylene glycol (HO-CH2-CH2-O-CH2-CH2-OH) as a product.

5. **Evaluate Other Options**:
Aqueous KOH is a base and would not facilitate the formation of diethylene glycol from glycol. Therefore, it can be ruled out. Concentrated sulfuric acid has already been determined to lead to dioxane.

6. **Conclusion**:
The correct reagent that leads to the formation of diethylene glycol from glycol upon heating is concentrated phosphoric acid (H3PO4). Thus, the answer is option B.

### Final Answer:
Diethylene glycol is obtained by heating glycol with concentrated H3PO4 (option B).

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