Which of the following substances is not an isomer of 3-ethyl 2-methyl pentane?

Options

A.
B.
C.
D. All are isomers

Explanation

To determine which of the given substances is not an isomer of 3-ethyl-2-methylpentane, we need to follow these steps:

### Step 1: Draw the structure of 3-ethyl-2-methylpentane
1. Identify the main carbon chain, which is pentane (5 carbon atoms).
2. Number the carbon chain from one end to the other.
3. At the second carbon (C-2), attach a methyl group (CH₃).
4. At the third carbon (C-3), attach an ethyl group (C₂H₅).

The structure can be represented as follows:
```
CH3
|
CH3-CH-CH-CH2-CH3
|
CH2-CH3
```

### Step 2: Count the number of carbon and hydrogen atoms
- **Carbons (C)**: 5 (from pentane) + 1 (from methyl) + 2 (from ethyl) = 8 carbon atoms.
- **Hydrogens (H)**: The total number of hydrogens can be calculated based on the structure. For 3-ethyl-2-methylpentane, the total is 18 hydrogen atoms.

### Step 3: Analyze the options
Now, we will analyze the options provided to see which one does not match the carbon and hydrogen count of 3-ethyl-2-methylpentane.

1. **Option A**: Count the carbons and hydrogens.
- Carbons: 8
- Hydrogens: 18
- This is a valid isomer.

2. **Option B**: Count the carbons and hydrogens.
- Carbons: 7
- Hydrogens: 16
- This does not match the count for 3-ethyl-2-methylpentane.

3. **Option C**: Count the carbons and hydrogens.
- Carbons: 8
- Hydrogens: 18
- This is also a valid isomer.

### Conclusion
Based on the analysis, **Option B** is not an isomer of 3-ethyl-2-methylpentane because it has 7 carbons and 16 hydrogens, which does not match the original compound's formula.