Which of the following is most acidic?

Options

A.
B.
C. `CH_(3)-O-H`
D.

Answer

To determine which of the given molecules is the most acidic, we need to analyze the stability of their conjugate bases after they lose a proton (H⁺). The acidity of a compound is directly related to the stability of its conjugate base; a more stable conjugate base corresponds to a stronger acid.

### Step-by-Step Solution:

1. **Identify the Molecules**: We have four options (A, B, C, D) with different functional groups. We need to analyze each one to see how they behave when they lose a proton.

2. **Analyze Option A**:
- When the molecule in option A loses a proton, it forms a conjugate base with a negative charge on nitrogen.
- The positive charge on nitrogen is neutralized, which contributes to the stability of the conjugate base.

3. **Analyze Option B**:
- In option B, the proton is lost from the oxygen atom, resulting in a conjugate base with a negative charge on oxygen.
- The positive charge on oxygen is neutralized, and since oxygen is more electronegative than nitrogen, this conjugate base is relatively stable.

4. **Analyze Option C**:
- Here, the molecule loses a proton to form a conjugate base with a negative charge on oxygen (CH₃O⁻).
- However, the presence of the methyl group (CH₃) is electron-donating (due to the +I effect), which destabilizes the conjugate base, making it less stable.

5. **Analyze Option D**:
- In option D, the proton is lost from nitrogen, resulting in a conjugate base with a negative charge on nitrogen.
- Similar to option A, the positive charge on nitrogen is neutralized, contributing to the stability of the conjugate base.

6. **Compare Stability of Conjugate Bases**:
- From the analysis:
- Option A: Stable (neutralizes positive charge on N)
- Option B: Stable (neutralizes positive charge on O and O is more electronegative)
- Option C: Unstable (electron-donating effect destabilizes the conjugate base)
- Option D: Stable (neutralizes positive charge on N)

7. **Determine the Most Acidic Molecule**:
- Since option B has the most stable conjugate base due to the high electronegativity of oxygen, it is the most acidic among the four options.

### Conclusion:
The most acidic molecule is from **Option B**.

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