Which of the following options shows the correct order of decreasing acidity:

Options

A. `PhCO_(2)H gt PhSO_(3)H gt PhCH_(2)H gt PhOH`
B. `PhSO_(3)H gt PhOH gt PhCH_(2)H gt PhCO_(2)H`
C. `PhCO_(2)H gt PhOH gt PhCH_(2)H gt PhSO_(3)H`
D. `PhSO_(3)H gt PhCO_(2)H gt PhOH gt PhCH_(2)H`

Answer

To determine the correct order of decreasing acidity among the given groups, we need to analyze the acidity of each group attached to a phenyl ring (Ph). The groups we are considering are:

1. SO3H (sulfonic acid)
2. COOH (carboxylic acid)
3. OH (hydroxyl group)
4. CH3 (methyl group)

### Step-by-step solution:

1. **Identify the Groups**: We have the following groups attached to a phenyl ring:
- Ph-SO3H
- Ph-COOH
- Ph-OH
- Ph-CH3

2. **Assess Acidity**:
- **Ph-SO3H**: Sulfonic acid is a very strong acid due to the presence of the sulfonyl group (SO2) which stabilizes the negative charge of its conjugate base (Ph-SO3^-). This makes it the most acidic group.
- **Ph-COOH**: Carboxylic acids are also acidic, but they are less acidic than sulfonic acids. The conjugate base (Ph-COO^-) is stabilized by resonance, but not as effectively as the sulfonate ion.
- **Ph-OH**: The hydroxyl group can donate a proton, but the resulting phenoxide ion (Ph-O^-) is less stable than the carboxylate ion (Ph-COO^-). Therefore, it is less acidic than carboxylic acids.
- **Ph-CH3**: The methyl group is an electron-donating group, which decreases acidity. It does not stabilize the negative charge of the conjugate base (Ph-CH2^-) and is therefore the least acidic.

3. **Rank the Groups**: Based on the analysis:
- Most acidic: Ph-SO3H
- Less acidic: Ph-COOH
- Even less acidic: Ph-OH
- Least acidic: Ph-CH3

4. **Final Order**: The correct order of decreasing acidity is:
- Ph-SO3H > Ph-COOH > Ph-OH > Ph-CH3

### Conclusion:
The correct option that shows the order of decreasing acidity is:
- **Ph-SO3H > Ph-COOH > Ph-OH > Ph-CH3**