Which of the following is not a Lewis base ?

Options

A. `CH_(4)`
B. `CN^(-)`
C. `ROH`
D. `NH_(3)`

Explanation

To determine which of the following options is not a Lewis base, we need to understand the definition of a Lewis base. A Lewis base is defined as a species that can donate a pair of electrons. Therefore, we need to identify which of the given options lacks the ability to donate electrons.

### Step-by-Step Solution:

1. **Identify the Options**: We need to analyze the given options. Let's consider the options provided: Methane (CH₄), Cyanide ion (CN⁻), Alcohol (ROH), and Ammonia (NH₃).

2. **Analyze Methane (CH₄)**:
- Methane consists of one carbon atom bonded to four hydrogen atoms.
- In methane, all four valence electrons of carbon are involved in bonding with hydrogen atoms.
- There are no lone pairs of electrons available on carbon to donate.
- **Conclusion**: Methane cannot act as a Lewis base.

3. **Analyze Cyanide Ion (CN⁻)**:
- The cyanide ion has a nitrogen atom bonded to a carbon atom, and it carries a negative charge.
- Nitrogen has a lone pair of electrons that can be donated.
- **Conclusion**: CN⁻ can act as a Lewis base.

4. **Analyze Alcohol (ROH)**:
- In alcohols, the oxygen atom has two lone pairs of electrons.
- These lone pairs can be donated by the oxygen atom.
- **Conclusion**: Alcohol (ROH) can act as a Lewis base.

5. **Analyze Ammonia (NH₃)**:
- Ammonia consists of a nitrogen atom bonded to three hydrogen atoms.
- Nitrogen has one lone pair of electrons that can be donated.
- **Conclusion**: Ammonia (NH₃) can act as a Lewis base.

6. **Final Conclusion**:
- Among the options analyzed, only Methane (CH₄) does not have any lone pairs of electrons available for donation.
- Therefore, the answer to the question "Which of the following is not a Lewis base?" is **Methane (CH₄)**.