Which of the following is the strongest base ?

Options

A. `C_(6)H_(5)NH_(2)(pK_(b)=9.42)`
B. `C_(6)H_(5)NHCH_(3)(pK_(b)=9.15)`
C. `C_(6)H_(5)N(CH_(3))_(2)(pK_(b)=8.94)`
D. `C_(6)H_(5)NHC_(2)H_(5)(pK_(b)=8.89)`

Explanation

To determine which of the given options is the strongest base, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of pKb**:
- pKb is the negative logarithm of the base dissociation constant (Kb). It is given by the formula:
\[ \text{pKb} = -\log(Kb) \]
- A lower pKb value indicates a stronger base because it corresponds to a higher Kb value, meaning the base dissociates more in solution to produce hydroxide ions (OH⁻).

2. **Compare pKb Values**:
- We need to look at the pKb values of the bases provided in the options. The base with the lowest pKb value will be the strongest base.

3. **Identify the Lowest pKb**:
- Review the pKb values given for each option. Identify which one has the lowest value.

4. **Conclusion**:
- The option with the lowest pKb value is the strongest base among the options provided.

### Example:
Assuming the options provided were:
- Option A: pKb = 5
- Option B: pKb = 3
- Option C: pKb = 7
- Option D: pKb = 2

From the above values:
- The lowest pKb is for Option D (pKb = 2).

Thus, **Option D** is the strongest base.