Ammonia is a Lewis base. It forms complexes with cations. Which one of the following cations does not form complex with ammonia?

Options

A. `Ag^(+)`
B. `Cu^(2+)`
C. `Cd^(2+)`
D. `Pb^(2+)`

Answer

To determine which cation does not form a complex with ammonia, we need to analyze the nature of the cations provided in the options.

### Step-by-Step Solution:

1. **Understanding Lewis Bases and Complex Formation**:
- Ammonia (NH₃) is a Lewis base, meaning it can donate a pair of electrons to form a coordinate bond with a cation (Lewis acid).
- Complex formation typically occurs with cations that have empty d-orbitals, allowing them to accept electron pairs from Lewis bases.

2. **Identifying the Cations**:
- The cations given are: Ag⁺ (Silver), Cu²⁺ (Copper), Cd²⁺ (Cadmium), and Pb²⁺ (Lead).
- We need to check which of these cations can form complexes with ammonia.

3. **Analyzing Each Cation**:
- **Ag⁺ (Silver)**: This is a d-block element and can form complexes with ammonia. For example, it can form [Ag(NH₃)₂]⁺.
- **Cu²⁺ (Copper)**: Also a d-block element, it readily forms complexes with ammonia, such as [Cu(NH₃)₄]²⁺.
- **Cd²⁺ (Cadmium)**: This is a d-block element as well and can form complexes with ammonia, like [Cd(NH₃)₄]²⁺.
- **Pb²⁺ (Lead)**: Lead is a p-block element and does not have the same tendency to form complexes with ammonia. Instead, it tends to form precipitates when reacted with ammonia.

4. **Conclusion**:
- Among the given cations, Pb²⁺ (Lead) does not form a complex with ammonia due to its nature as a p-block element, which lacks the necessary d-orbitals for complex formation.

### Final Answer:
**Pb²⁺ (Lead) does not form a complex with ammonia.**

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