Which of the following acids combines the properties of an aldehyde and an acid ?

Options

A. Benzoic acid
B. Acetic acid
C. Formic acid
D. Oxalic acid

Answer

To determine which acid combines the properties of both an aldehyde and a carboxylic acid, we will analyze the given options one by one.

### Step-by-Step Solution:

1. **Understand the Functional Groups**:
- Aldehydes contain the functional group -CHO.
- Carboxylic acids contain the functional group -COOH.

2. **Analyze Option 1: Benzoic Acid**:
- Structure: C6H5COOH (Benzene ring with a carboxylic acid group).
- Properties: Benzoic acid only shows acidic properties due to the presence of the -COOH group and does not have an aldehyde group.
- Conclusion: **Does not combine both properties**.

3. **Analyze Option 2: Acetic Acid**:
- Structure: CH3COOH (Methyl group attached to a carboxylic acid group).
- Properties: Acetic acid also only shows acidic properties as it has the -COOH group and lacks an aldehyde group.
- Conclusion: **Does not combine both properties**.

4. **Analyze Option 3: Formic Acid**:
- Structure: HCOOH (Contains both -CHO and -COOH groups).
- Properties: Formic acid has the -COOH group (carboxylic acid) and the -CHO group (aldehyde). Therefore, it exhibits properties of both an aldehyde and an acid.
- Conclusion: **Combines both properties**.

5. **Analyze Option 4: Oxalic Acid**:
- Structure: HOOC-COOH (Two carboxylic acid groups).
- Properties: Oxalic acid contains two -COOH groups and does not have an aldehyde group.
- Conclusion: **Does not combine both properties**.

### Final Answer:
The acid that combines the properties of both an aldehyde and an acid is **Formic Acid (HCOOH)**.

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