Which of the following is an example of elimination reaction?

Options

A. Chlorination of methane
B. Dehydration of ethanol
C. Nitration of benzene
D. Hydroxylation of ethylene

Explanation

To determine which of the given reactions is an example of an elimination reaction, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Identify the Reactions**: We have four reactions to analyze. Let's denote them as:
- Reaction A: Chlorination of Methane
- Reaction B: Dehydration of Ethanol
- Reaction C: Nitration of Benzene
- Reaction D: Hydroxylation of Ethylene

2. **Analyze Reaction A (Chlorination of Methane)**:
- The reaction involves methane (CH₄) reacting with chlorine (Cl₂) to produce chloromethane (CH₃Cl) and hydrogen chloride (HCl).
- This reaction is a free radical substitution reaction, not an elimination reaction.
- **Conclusion**: Reaction A is not an elimination reaction.

3. **Analyze Reaction B (Dehydration of Ethanol)**:
- The structure of ethanol is CH₃CH₂OH.
- When ethanol undergoes dehydration (removal of water), it produces ethylene (CH₂=CH₂) by eliminating a water molecule (H₂O).
- This process fits the definition of an elimination reaction, where a small molecule (H₂O) is removed from a larger molecule.
- **Conclusion**: Reaction B is an elimination reaction.

4. **Analyze Reaction C (Nitration of Benzene)**:
- In this reaction, benzene (C₆H₆) reacts with concentrated sulfuric acid (H₂SO₄) and nitric acid (HNO₃) to form nitrobenzene (C₆H₅NO₂).
- This reaction involves the substitution of a hydrogen atom in benzene with a nitro group (NO₂), which is characteristic of electrophilic substitution reactions.
- **Conclusion**: Reaction C is not an elimination reaction.

5. **Analyze Reaction D (Hydroxylation of Ethylene)**:
- Ethylene (CH₂=CH₂) reacts with a reagent (like KMnO₄) to form a diol (CH₂(OH)-CH₂(OH)).
- This reaction involves the addition of hydroxyl groups across the double bond, which is an addition reaction, not an elimination reaction.
- **Conclusion**: Reaction D is not an elimination reaction.

### Final Answer:
The only reaction that qualifies as an elimination reaction is **Reaction B: Dehydration of Ethanol**.