Consider following acid
`underset(I)(ClCH_(2)COOH)," "underset(II)(CH_(3)COOH)," "underset(III)(CH_(3)CH_(2)COOH)`
Correct order of their pH value

Options

A. `III lt II lt I`
B. `I lt II lt III`
C. `I lt III lt II`
D. `II lt I lt III`

Answer

To determine the correct order of pH values for the given acids, we need to analyze their acidic strengths based on their conjugate bases. The acids in question are:

1. ClCH₂COOH (I)
2. CH₃COOH (II)
3. CH₃CH₂COOH (III)

### Step 1: Identify the Conjugate Bases
The first step is to identify the conjugate bases of each acid:

- For ClCH₂COOH, the conjugate base is ClCH₂COO⁻.
- For CH₃COOH, the conjugate base is CH₃COO⁻.
- For CH₃CH₂COOH, the conjugate base is CH₃CH₂COO⁻.

### Step 2: Analyze the Stability of Conjugate Bases
Next, we analyze the stability of these conjugate bases, as the stability is directly related to the strength of the corresponding acid:

1. **ClCH₂COO⁻**: The presence of the electronegative chlorine atom exerts a strong -I (inductive) effect, pulling electron density away from the carboxylate group. This stabilizes the negative charge on the conjugate base, making it a strong acid.

2. **CH₃COO⁻**: The methyl group (CH₃) has a +I (inductive) effect, which increases electron density on the carboxylate group, making the conjugate base less stable compared to ClCH₂COO⁻. Thus, CH₃COOH is a weaker acid than ClCH₂COOH.

3. **CH₃CH₂COO⁻**: The ethyl group (CH₃CH₂) also has a +I effect, which is even stronger than that of the methyl group. This leads to a further increase in electron density on the carboxylate group, making the conjugate base less stable than CH₃COO⁻. Therefore, CH₃CH₂COOH is the weakest acid among the three.

### Step 3: Determine the Order of Acidity
From the analysis, we can summarize the strength of the acids:

- ClCH₂COOH (I) is the strongest acid, resulting in the lowest pH.
- CH₃COOH (II) is a weaker acid than ClCH₂COOH, resulting in a higher pH.
- CH₃CH₂COOH (III) is the weakest acid, resulting in the highest pH.

### Conclusion: Order of pH Values
Thus, the correct order of their pH values from lowest to highest is:

**ClCH₂COOH (I) < CH₃COOH (II) < CH₃CH₂COOH (III)**