Which of the following is stronger acid than methanol?

Options

A. `CH_(3) - C -= CH`
B.
C.
D. `H_(3)C - underset(H)underset(|)O^(+)-H`

Explanation

To determine which of the given options is a stronger acid than methanol, we need to analyze each option in relation to methanol's acidity.

### Step-by-Step Solution:

1. **Understand Methanol's Structure and Acidity**:
- Methanol (CH₃OH) is a weak acid. Its acidity is primarily due to the ability to donate a proton (H⁺) from the hydroxyl (-OH) group.

2. **Analyze Each Option**:
- **Option A**: Alkene/Alkyne
- Alkenes and alkynes are generally not acidic. They do not have a hydroxyl group to donate a proton, making them weaker acids than methanol.
- **Option B**: Secondary Alcohol
- Secondary alcohols (like isopropanol) are also weak acids, similar to methanol. They do not exhibit stronger acidity than methanol.
- **Option C**: Tertiary Alcohol
- Tertiary alcohols are slightly more acidic than primary and secondary alcohols but still do not surpass the acidity of methanol significantly.
- **Option D**: Protonated Methanol
- Protonated methanol (CH₃OH₂⁺) is methanol that has accepted an additional proton (H⁺). This makes it a stronger acid because it can readily donate this extra proton.

3. **Conclusion**:
- Among the given options, only **Option D (Protonated Methanol)** is a stronger acid than methanol itself. This is because the addition of a proton increases the likelihood of donating a proton, thus enhancing acidity.

### Final Answer:
**Option D: Protonated Methanol** is stronger than methanol.