Arrange the following alkyl halides in order of dehydrohalogenation, `C_2H_5I,C_2H_5Cl,C_2H_5Br,C_2H_5F`

Options

A. `C_2H_5F gt C_2H_5Cl gt C_2H_5Br gt C_2H_5I`
B. `C_2H_5I gt C_2H_5Br gt C_2H_5Cl gt C_2H_5F`
C. `C_2H_5I gt C_2H_5Cl gt C_2H_5Br gt C_2H_5F`
D. `C_2H_5F gt C_2H_5I gt C_2H_5Br gt C_2H_5Cl`

Answer

To arrange the alkyl halides \(C_2H_5I\), \(C_2H_5Cl\), \(C_2H_5Br\), and \(C_2H_5F\) in order of their dehydrohalogenation, we need to consider the stability of the leaving groups during the reaction. The process involves the removal of HX (where X is the halogen) from the alkyl halide to form an alkene.

### Step-by-Step Solution:

1. **Identify the Alkyl Halides**:
- The alkyl halides given are:
- Ethyl iodide (\(C_2H_5I\))
- Ethyl bromide (\(C_2H_5Br\))
- Ethyl chloride (\(C_2H_5Cl\))
- Ethyl fluoride (\(C_2H_5F\))

2. **Understand Dehydrohalogenation**:
- Dehydrohalogenation is the elimination of HX from the alkyl halide, leading to the formation of an alkene. The rate of this reaction depends on how easily the halogen can leave as a halide ion (X⁻).

3. **Evaluate the Leaving Groups**:
- The ability of a halogen to leave is influenced by its size and electronegativity. The order of leaving group ability from best to worst is:
- Iodide (I⁻) > Bromide (Br⁻) > Chloride (Cl⁻) > Fluoride (F⁻)

4. **Rank the Alkyl Halides**:
- Based on the leaving group ability:
- Ethyl iodide (\(C_2H_5I\)) has iodide, which is the best leaving group.
- Ethyl bromide (\(C_2H_5Br\)) has bromide, which is the second-best leaving group.
- Ethyl chloride (\(C_2H_5Cl\)) has chloride, which is the third-best leaving group.
- Ethyl fluoride (\(C_2H_5F\)) has fluoride, which is the worst leaving group.

5. **Final Order of Dehydrohalogenation**:
- Therefore, the order of dehydrohalogenation from fastest to slowest is:
- \(C_2H_5I\) > \(C_2H_5Br\) > \(C_2H_5Cl\) > \(C_2H_5F\)

### Conclusion:
The final order of dehydrohalogenation for the given alkyl halides is:
- **Ethyl iodide > Ethyl bromide > Ethyl chloride > Ethyl fluoride**