Among the following the lowest `pK_(a)` value is of :

Options

A. `CH_(3)COOH`
B. `HCOOH`
C. `(CH_(3))_(2)CHCOOH`
D. `CH_(3)CH_(2)COOH`

Explanation

To determine which compound has the lowest pKa value among the given options, we need to identify the strongest acid. The pKa value is inversely related to the strength of the acid; the lower the pKa, the stronger the acid.

### Step-by-Step Solution:

1. **Understand pKa and Acid Strength**:
- pKa is a measure of the acidity of a compound. A lower pKa value indicates a stronger acid.
- The strength of an acid can be influenced by the presence of electron-withdrawing or electron-releasing groups.

2. **Identify Electron-Withdrawing and Electron-Releasing Groups**:
- Electron-withdrawing groups (EWGs) increase acidity by stabilizing the negative charge on the conjugate base.
- Electron-releasing groups (ERGs) decrease acidity by destabilizing the conjugate base.

3. **Analyze the Given Options**:
- For each compound, identify the functional groups and their effects on acidity.
- For example, if one of the options is formic acid (HCOOH), it has a carboxylic acid group without any strong electron-releasing groups attached.

4. **Compare the Acidity of Each Compound**:
- If one compound has alkyl groups (which are ERGs), it will likely have a higher pKa (weaker acid).
- In contrast, compounds with more electron-withdrawing groups will have lower pKa values (stronger acids).

5. **Determine the Strongest Acid**:
- After analyzing the effects of various groups, identify which compound has the highest acidity.
- In this case, formic acid (HCOOH) is identified as the strongest acid among the options.

6. **Conclusion**:
- Since formic acid has the lowest pKa value due to its strong acidic nature, it is the correct answer.

### Final Answer:
The compound with the lowest pKa value is **formic acid (HCOOH)**.

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