Acid strength is measured by the position of equilibrium of ionization in water. In other words acid strength is the function of the stability of conjugate base of the acid. More is the stability of conjugate base of the acid, more is the acidity of acid.
Which of the following is weakest acid?

Options

A.
B.
C.
D.

Answer

To determine which of the given acids is the weakest, we need to analyze the stability of their conjugate bases. The weaker the acid, the less stable its conjugate base will be. Here’s a step-by-step solution:

### Step 1: Identify the Acids
Assume we have four acids (let's denote them as Acid A, Acid B, Acid C, and Acid D). We will analyze the conjugate bases formed when these acids lose a proton (H⁺).

### Step 2: Write the Conjugate Bases
For each acid, remove an H⁺ ion to find the conjugate base:
- **Acid A**: Conjugate base A⁻
- **Acid B**: Conjugate base B⁻
- **Acid C**: Conjugate base C⁻
- **Acid D**: Conjugate base D⁻

### Step 3: Analyze the Stability of Conjugate Bases
1. **Conjugate Base A⁻**: Check the structure and resonance. If it has multiple resonance forms, it is likely more stable.
2. **Conjugate Base B⁻**: Similarly, analyze the resonance and inductive effects. If it has strong electron-withdrawing groups, it may be more stable.
3. **Conjugate Base C⁻**: Look for resonance and the presence of electronegative atoms that can stabilize the negative charge.
4. **Conjugate Base D⁻**: Assess the structure for resonance and intramolecular hydrogen bonding, which can enhance stability.

### Step 4: Compare Stability
- The conjugate base with the most resonance structures and/or stabilizing effects (like intramolecular hydrogen bonding) will be the most stable.
- The conjugate base with the least resonance and less ability to stabilize the negative charge will be the least stable.

### Step 5: Determine the Weakest Acid
Since the weakest acid corresponds to the least stable conjugate base, identify which conjugate base is the least stable based on your analysis.

### Conclusion
After analyzing the conjugate bases, if Conjugate Base A⁻ is found to be the least stable due to having a negative charge localized on one oxygen without significant resonance or stabilizing effects, then Acid A is the weakest acid.

### Final Answer
The weakest acid is **Acid A** (Option 1).

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