Which of the following is a pair of functional group isomers?

Options

A.
B.
C.
D. `CH_3-oversetoverset(O)(||)C-H` & `CH_3-oversetoverset(O)(||)C-CH_3`

Answer

To determine which of the following is a pair of functional group isomers, we need to understand what functional group isomers are. Functional group isomers are compounds that have the same molecular formula but different functional groups.

### Step-by-Step Solution:

1. **Identify the Functional Groups**:
- First, we need to identify the functional groups in the options provided. Common functional groups to consider include aldehydes, ketones, carboxylic acids, esters, alcohols, and ethers.

2. **List the Known Functional Group Isomer Pairs**:
- The well-known pairs of functional group isomers include:
- Aldehydes and Ketones
- Carboxylic Acids and Esters
- Alcohols and Ethers

3. **Analyze Each Option**:
- **Option 1**: Chlorine and Bromine - These are halogens and not functional group isomers.
- **Option 2**: OCH3 (methoxy) and OC2H5 (ethoxy) - Both are ethers, hence not functional group isomers.
- **Option 3**: Alcohol and Phenol - While they are different, they do not represent a functional group isomer pair as alcohols pair with ethers.
- **Option 4**: Aldehyde and Ketone - Aldehydes (RCHO) and Ketones (RC(=O)R') are indeed functional group isomers.

4. **Conclusion**:
- Based on the analysis, the correct answer is the pair of Aldehyde and Ketone, as they have the same molecular formula but different functional groups.

### Final Answer:
The pair of functional group isomers is Aldehyde and Ketone.

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