Choose the strongest base among the following:

Options

A.
B.
C.
D.

Explanation

To determine the strongest base among the given options, we need to analyze the availability of the lone pairs of electrons on the nitrogen atoms in each structure. The more available the lone pair, the stronger the base.

### Step-by-Step Solution:

1. **Identify the Structures**:
- Let's denote the compounds as A, B, C, and D. Each compound has a nitrogen atom with a lone pair.

2. **Analyze Resonance Effects**:
- **Compound A**: The nitrogen's lone pair can participate in resonance with the aromatic ring, making it less available for protonation.
- **Compound B**: Similar to A, the lone pair on nitrogen can also participate in resonance with the ring, reducing its basicity.
- **Compound C**: The lone pair on nitrogen can participate in resonance, but it is slightly more available than in A and B due to the structure.
- **Compound D**: The lone pair on nitrogen is not involved in resonance with any ring or double bond, making it fully available for donation.

3. **Compare Basicity**:
- Since the lone pairs in compounds A, B, and C are involved in resonance, they are less available for bonding with protons (H⁺).
- In contrast, the lone pair in compound D is not involved in resonance, making it the most available for protonation.

4. **Conclusion**:
- Based on the analysis, compound D has the most available lone pair and is therefore the strongest base among the options provided.

### Final Answer:
The strongest base among the given options is **D**.