Among the following the strongest acid is

Options

A. (a) `CH_3COOH`
B. (b) `CH_2ClCH_2COOH`
C. (c) `CH_2ClCOOH`
D. (d) `CH_3CH_2COOH`

Explanation

To determine which of the given acids is the strongest, we need to analyze the structure of each acid and understand how their substituents affect their acidity. The key concepts to consider are the inductive effects of the substituents on the carboxylic acid group (-COOH).

### Step-by-Step Solution:

1. **Identify the Acids**: The acids provided are:
- A: CH3COOH (Acetic acid)
- B: CH2ClCH2COOH (Chloroacetic acid with a chlorine on the second carbon)
- C: CH2ClCOOH (Chloroacetic acid with a chlorine on the first carbon)
- D: CH3CH2COOH (Propanoic acid)

2. **Understand Inductive Effects**:
- **+I Effect (Positive Inductive Effect)**: Alkyl groups (like CH3 and CH2CH3) donate electron density towards the carboxylic acid group, making it harder to lose a proton (H+). This decreases acidity.
- **-I Effect (Negative Inductive Effect)**: Electronegative atoms (like Cl) withdraw electron density from the carboxylic acid group, making it easier to lose a proton. This increases acidity.

3. **Analyze Each Acid**:
- **Acetic Acid (CH3COOH)**: The CH3 group exhibits a +I effect, which decreases its acidity.
- **Propanoic Acid (CH3CH2COOH)**: The CH2CH3 group also exhibits a +I effect, but it is stronger than that of CH3. Thus, it is less acidic than acetic acid.
- **Chloroacetic Acid (CH2ClCOOH)**: The chlorine atom exhibits a -I effect, which increases acidity. The chlorine is directly attached to the carbon adjacent to the carboxylic group, enhancing its effect.
- **Chloroacetic Acid (CH2ClCH2COOH)**: The chlorine is further away from the carboxylic group compared to CH2ClCOOH, which means its -I effect is weaker.

4. **Compare Acidity**:
- Between acetic acid and propanoic acid, acetic acid is stronger due to the lesser +I effect.
- Between the two chloroacetic acids, CH2ClCOOH (with chlorine closer to the carboxylic group) is stronger than CH2ClCH2COOH.
- Therefore, the order of acidity from strongest to weakest is:
- CH2ClCOOH > CH2ClCH2COOH > CH3COOH > CH3CH2COOH

5. **Conclusion**: The strongest acid among the given options is CH2ClCOOH (Chloroacetic acid), which corresponds to option C.

### Final Answer:
**The strongest acid is CH2ClCOOH (option C).**