An isomer of ethanol is:

Options

A. Methanol
B. Diethyl ether
C. Acetone
D. Dimethyl ether

Explanation

To find an isomer of ethanol, we need to identify a compound that has the same molecular formula as ethanol but a different structure. The molecular formula for ethanol is C2H6O.

### Step-by-Step Solution:

1. **Identify the Molecular Formula of Ethanol**:
- Ethanol has the molecular formula C2H6O.

2. **List the Options Given**:
- Methanol (CH3OH)
- Diethyl ether (C2H5)2O
- Acetone (C3H6O)
- Dimethyl ether (CH3OCH3)

3. **Evaluate Each Option**:
- **Methanol (CH3OH)**: This has a different molecular formula (C1H4O) and is not an isomer of ethanol.
- **Diethyl ether (C2H5)2O**: This has a molecular formula of C4H10O, which is not the same as ethanol (C2H6O).
- **Acetone (C3H6O)**: This has a different molecular formula (C3H6O) and is not an isomer of ethanol.
- **Dimethyl ether (CH3OCH3)**: This has the molecular formula C2H6O, which is the same as ethanol but has a different structure.

4. **Conclusion**:
- Among the options, dimethyl ether is the only compound that has the same molecular formula as ethanol (C2H6O) but a different structure, making it an isomer of ethanol.

### Final Answer:
The isomer of ethanol is **Dimethyl ether (CH3OCH3)**.