Which of the following is strongest acid among following

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds is the strongest acid, we need to analyze the effects of the substituents on the carboxylic acid. The strength of an acid is often related to the stability of its conjugate base after the acid donates a proton (H⁺). Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Compounds
We have four compounds with different substituents in the para position of a carboxylic acid:
1. Carboxylic acid with -OH (hydroxyl group)
2. Carboxylic acid with -NO2 (nitro group)
3. Carboxylic acid with -SO3H (sulfonic acid group)
4. Carboxylic acid with -CH3 (methyl group)

### Step 2: Understand Acid Strength
The strength of an acid is determined by the stability of its conjugate base after it loses a proton (H⁺). A more stable conjugate base corresponds to a stronger acid.

### Step 3: Analyze the Substituents
- **-NO2 (Nitro group)**: This is a strong electron-withdrawing group. It stabilizes the negative charge on the conjugate base through resonance and inductive effects.
- **-SO3H (Sulfonic acid group)**: This is also a strong electron-withdrawing group, but not as strong as -NO2.
- **-OH (Hydroxyl group)**: This group is weakly electron-withdrawing through resonance but can also donate electrons, making it less effective in stabilizing the conjugate base.
- **-CH3 (Methyl group)**: This is an electron-donating group, which destabilizes the conjugate base by increasing electron density.

### Step 4: Compare the Effects
Based on the electron-withdrawing strength:
1. -NO2 is the strongest electron-withdrawing group, thus stabilizing the conjugate base the most.
2. -SO3H follows as a strong electron-withdrawing group.
3. -OH is weaker in comparison.
4. -CH3 is an electron-donating group, which destabilizes the conjugate base.

### Step 5: Conclusion
Since -NO2 provides the greatest stabilization to the conjugate base, the carboxylic acid with the -NO2 substituent is the strongest acid among the given options.

### Final Answer
The strongest acid among the given options is the carboxylic acid with the -NO2 (nitro group) in the para position.

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