`Cd^(2+)` and `Cu^(2+)` are seprated by (a) ___formation using (b) ___in which (c ) is more stable then (d ) ____ . On passing `H_(2)S` gas (e ) ____. Is precipitate.

Answer

To solve the question regarding the separation of `Cd^(2+)` and `Cu^(2+)`, we can break it down step by step.

### Step-by-Step Solution:

1. **Identify the Separation Method**:
The separation of `Cd^(2+)` and `Cu^(2+)` is achieved through a specific chemical process. The correct term for this process is **complex formation**.

**Answer for (a)**: Complex formation

2. **Identify the Reagent Used**:
The reagent used for this separation is **potassium cyanide (KCN)**. This reagent helps in forming stable complexes with copper ions while forming unstable complexes with cadmium ions.

**Answer for (b)**: KCN

3. **Determine Stability of Complexes**:
In this context, the complex formed with copper is more stable than the complex formed with cadmium. Therefore, we can denote the copper complex as **C** and the cadmium complex as **D**.

**Answer for (c)**: Copper complex (Cu complex)
**Answer for (d)**: Cadmium complex (K2Cd(CN)4)

4. **Reaction with H2S**:
When hydrogen sulfide (H2S) gas is passed through the solution, it leads to the precipitation of cadmium sulfide (CdS), which is an insoluble compound.

**Answer for (e)**: Cadmium sulfide (CdS)

### Final Answers:
- (a) Complex formation
- (b) KCN
- (c) Copper complex
- (d) Cadmium complex (K2Cd(CN)4)
- (e) Cadmium sulfide (CdS)