The moelcule having a formyl group is

Options

A. acetone
B. acetaldehyde
C. acetic acid
D. acetic anhydride

Explanation

To determine which molecule has a formyl group, we first need to understand what a formyl group is.

### Step-by-Step Solution:

1. **Definition of Formyl Group**:
A formyl group is defined as a carbonyl group (C=O) that is bonded to a hydrogen atom (H). The structure can be represented as -CHO.

2. **Analyzing Each Option**:
- **Option A: Acetone**
- Structure: CH₃C(=O)CH₃
- Analysis: Acetone has a carbonyl group, but it is not bonded to a hydrogen atom. Therefore, it does not contain a formyl group.

- **Option B: Acetaldehyde**
- Structure: CH₃C(=O)H
- Analysis: Acetaldehyde has a carbonyl group bonded to a hydrogen atom. Thus, it contains a formyl group.

- **Option C: Acetic Acid**
- Structure: CH₃C(=O)OH
- Analysis: Acetic acid has a carbonyl group, but it is bonded to a hydroxyl group (OH) instead of a hydrogen atom. Therefore, it does not contain a formyl group.

- **Option D: Acetic Anhydride**
- Structure: (CH₃C(=O))₂O
- Analysis: Acetic anhydride does not have a carbonyl group bonded to a hydrogen atom. Thus, it does not contain a formyl group.

3. **Conclusion**:
After analyzing all the options, the only molecule that contains a formyl group is **Option B: Acetaldehyde**.

### Final Answer:
**B: Acetaldehyde**