The most acidic of the following is

Options

A. `ClCH_(2)`COOH
B. `C_(6)H_(5)`COOH
C. `CD_(3)` COOH
D. `CH_(3)CH_(2)` COOH

Explanation

To determine the most acidic compound among the given options A, B, C, and D, we need to analyze the stability of the conjugate bases formed when each compound donates a proton (H+). The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Let's denote the compounds as follows:
- A: Compound with Cl (Chlorine)
- B: Compound with C₆H₅COOH (Benzoic acid)
- C: Compound with CD₃C=O (Deuterated ketone)
- D: Compound with C₂H₅COOH (Ethanoic acid)

2. **Understand Acidity**:
- Acidity is determined by the ability of a compound to donate a proton (H+). The stability of the resulting conjugate base (A-) is crucial. A more stable conjugate base corresponds to a stronger acid.

3. **Analyze the Conjugate Bases**:
- For each compound, we need to consider the stability of the conjugate base formed after losing H+.
- **Compound A**: The conjugate base will have a negative charge on oxygen, and the presence of Cl (an electron-withdrawing group) will stabilize this negative charge by pulling electron density away.
- **Compound B**: The conjugate base will also have a negative charge on oxygen. However, the stability is not significantly enhanced by any electron-withdrawing groups.
- **Compound C**: Similar to B, the negative charge on oxygen is not stabilized by any strong electron-withdrawing groups.
- **Compound D**: The presence of an alkyl group (C₂H₅) will increase electron density (due to +I effect), which destabilizes the negative charge on the conjugate base.

4. **Compare Stability**:
- **Stability of Conjugate Bases**:
- A: Stabilized by Cl (electron-withdrawing)
- B: No significant stabilization
- C: No significant stabilization
- D: Destabilized by alkyl group (electron-donating)
- Therefore, the stability order is: A > B = C > D.

5. **Conclusion**:
- Since compound A has the most stable conjugate base due to the electron-withdrawing effect of Cl, it is the most acidic among the given options.

### Final Answer:
The most acidic compound is **A**.