If the `pK_b` of a base is large, it is a strong base .

Explanation

To determine whether a large \( pK_b \) indicates a strong base, we need to understand the relationship between \( K_b \), \( pK_b \), and the strength of a base.

### Step-by-Step Solution:

1. **Understanding \( K_b \)**:
- The base dissociation constant (\( K_b \)) measures the strength of a base in solution. A larger \( K_b \) value indicates that the base dissociates more completely in water, producing more hydroxide ions (\( OH^- \)).
- For a base \( BOH \), the dissociation can be represented as:
\[ BOH \rightleftharpoons B^+ + OH^- \]
- The expression for \( K_b \) is:
\[ K_b = \frac{[B^+][OH^-]}{[BOH]} \]

2. **Understanding \( pK_b \)**:
- The \( pK_b \) is defined as:
\[ pK_b = -\log(K_b) \]
- This means that \( pK_b \) is inversely related to \( K_b \). If \( K_b \) is large, \( pK_b \) will be small, and vice versa.

3. **Relationship Between \( K_b \) and Base Strength**:
- A strong base will have a high \( K_b \) value, indicating that it dissociates significantly in solution.
- Consequently, a strong base will have a low \( pK_b \) value.

4. **Analyzing the Statement**:
- The statement in the question claims that if \( pK_b \) is large, it indicates a strong base. However, since a large \( pK_b \) corresponds to a small \( K_b \), this means that the base does not dissociate well in solution.
- Therefore, a large \( pK_b \) actually indicates a weak base, not a strong one.

5. **Conclusion**:
- The statement "If the \( pK_b \) of a base is large, it is a strong base" is **false**. A large \( pK_b \) indicates a weak base.