In which of the followinng functional group isomerism is not possible?

Options

A. Alcohols
B. Aldehdyes
C. Alkyl halides
D. Cyanides

Explanation

To determine in which of the following functional group isomerism is not possible, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Functional Group Isomerism**:
Functional group isomerism occurs when two or more compounds have the same molecular formula but different functional groups.

2. **Analyzing Option A (Alcohol and Ether)**:
- Alcohols (e.g., CH3CH2OH) and ethers (e.g., CH3OCH3) can have the same molecular formula (C2H6O).
- Therefore, functional group isomerism is possible between alcohols and ethers.

3. **Analyzing Option B (Aldehyde and Ketone)**:
- Aldehydes (e.g., CH3CHO) and ketones (e.g., CH3COCH3) can also share the same molecular formula (C3H6O).
- Hence, functional group isomerism is possible between aldehydes and ketones.

4. **Analyzing Option C (Cyanide and Isocyanide)**:
- Cyanides (e.g., CH3CN) and isocyanides (e.g., CH3N≡C) can have the same molecular formula (C2H5N).
- Thus, functional group isomerism is possible between cyanides and isocyanides.

5. **Analyzing Option D (Alkyl Halide)**:
- Alkyl halides (e.g., CH3CH2X, where X is a halogen) do not have a corresponding functional group that can form isomers with the same molecular formula.
- Therefore, functional group isomerism is **not possible** with alkyl halides.

6. **Conclusion**:
Based on the analysis, the correct answer is **Option D (Alkyl Halide)**, as it does not exhibit functional group isomerism with any other functional group.

### Final Answer:
Functional group isomerism is not possible in **Option D (Alkyl Halide)**.