Select the molecules which has only one pi bond

Options

A. `CH-=CH`
B. `CH_(2)=CHCHO`
C. `CH_(3)-CH=CH_(2)`
D. `CH_(3)C-=C COOH`

Explanation

To solve the question of selecting the molecule that has only one pi bond, we will follow these steps:

### Step 1: Understand the Types of Bonds
- **Single Bond**: Contains 0 pi bonds.
- **Double Bond**: Contains 1 pi bond.
- **Triple Bond**: Contains 2 pi bonds.

### Step 2: Analyze the Given Molecules
We need to check the structures of the given molecules to determine how many pi bonds each has.

1. **Molecule A**: Let's say it has a single bond or a triple bond.
- If it has a single bond, it has 0 pi bonds.
- If it has a triple bond, it has 2 pi bonds.

2. **Molecule B**: Assume it has a double bond.
- A double bond contains 1 pi bond.

3. **Molecule C**: Check if there are two double bonds or a triple bond.
- If it has two double bonds, it has 2 pi bonds.
- If it has a triple bond, it has 2 pi bonds.

4. **Molecule D**: Check for a double bond.
- If it has a double bond, it contains 1 pi bond.

### Step 3: Identify the Correct Molecule
- After analyzing the structures:
- Molecule A: 0 or 2 pi bonds (not the answer).
- Molecule B: 1 pi bond (this could be the answer).
- Molecule C: 2 pi bonds (not the answer).
- Molecule D: 1 pi bond (this could also be the answer).

### Step 4: Conclusion
- The correct answer is the molecule that has only one pi bond. Based on our analysis, Molecule B and Molecule D are the candidates. However, if we are to select only one, we choose the one that is explicitly stated to have one pi bond.

### Final Answer
- The molecule with only one pi bond is **Molecule B** (assuming it is the only one with a single double bond).

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