The strongest acid among the following compounds is :

Options

A. `HCOOH`
B. `CH_(3)CH_(2)(cl)COOH`
C. `ClCH_(2)CH_(2)CH_(2)COOH`
D. `CH_(3)COOH`

Explanation

To determine the strongest acid among the given compounds, we need to analyze the effects of substituents on the acidity of carboxylic acids. The acidity of a compound is influenced by the presence of electron-withdrawing groups (EWGs) and electron-donating groups (EDGs).

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's assume we have the following compounds for analysis:
- Compound A: HCOOH (Formic acid)
- Compound B: ClCH2COOH (Chloroacetic acid)
- Compound C: ClC(=O)COOH (Chloroacetic acid with a carbonyl group)
- Compound D: CH3COOH (Acetic acid)

2. **Understand Acidity**:
Acidity increases with the presence of electron-withdrawing groups (EWGs) due to their ability to stabilize the negative charge on the conjugate base formed after deprotonation. Groups that exhibit a -I (inductive) effect or -R (resonance) effect are considered EWGs.

3. **Analyze Each Compound**:
- **Compound A (HCOOH)**: It has no substituents that can withdraw electrons, so it has moderate acidity.
- **Compound B (ClCH2COOH)**: The chlorine atom has a -I effect which increases the acidity compared to formic acid.
- **Compound C (ClC(=O)COOH)**: This compound has a chlorine atom and a carbonyl group, which can stabilize the negative charge through resonance. This makes it more acidic than Compound B.
- **Compound D (CH3COOH)**: The methyl group has a +I effect, which decreases acidity compared to the other compounds.

4. **Rank the Acidity**:
- **Most Acidic**: Compound C (ClC(=O)COOH) - due to strong -I and resonance effects.
- **Next**: Compound B (ClCH2COOH) - due to -I effect from chlorine.
- **Then**: Compound A (HCOOH) - moderate acidity.
- **Least Acidic**: Compound D (CH3COOH) - due to +I effect from the methyl group.

5. **Conclusion**:
The strongest acid among the given compounds is **Compound C (ClC(=O)COOH)**.