`K_(4)[Fe(CN)_(6)]` can be used to detect one or more out of `Fe^(2+),Fe^(3+),Zn^(2+),Cu^(2+),Cd^(2+)`

Options

A. `Fe^(2+),Fe^(3+)`
B. `Fe^(3+),Zn^(+),Cu^(2+)`
C. all but `Fe^(2+)`
D. all but `Fe^(2+)`

Answer

To determine which cations can be detected using `K4[Fe(CN)6]`, we will analyze the reactions of this compound with each of the given cations: `Fe^(2+)`, `Fe^(3+)`, `Zn^(2+)`, `Cu^(2+)`, and `Cd^(2+)`.

### Step-by-Step Solution:

1. **Identify the Reagents**: The reagent in question is `K4[Fe(CN)6]`, also known as potassium ferrocyanide.

2. **Reactions with Cations**:
- **Copper (Cu²⁺)**: When `Cu²⁺` reacts with `K4[Fe(CN)6]`, it forms a reddish-brown precipitate of `Cu2[Fe(CN)6]`. This indicates that `Cu²⁺` can be detected using this reagent.
- **Cadmium (Cd²⁺)**: When `Cd²⁺` reacts with `K4[Fe(CN)6]`, it produces a bluish-white precipitate of `Cd2[Fe(CN)6]`. This shows that `Cd²⁺` can also be detected.
- **Iron (Fe³⁺)**: The reaction of `Fe³⁺` with `K4[Fe(CN)6]` results in the formation of a blue complex `Fe3[Fe(CN)6]`. This indicates that `Fe³⁺` can be detected as well.
- **Zinc (Zn²⁺)**: When `Zn²⁺` reacts with `K4[Fe(CN)6]`, it forms a white precipitate of `Zn2[Fe(CN)6]`. Thus, `Zn²⁺` can be detected using this reagent.
- **Iron (Fe²⁺)**: `Fe²⁺` does not form a distinct precipitate with `K4[Fe(CN)6]` and therefore cannot be detected using this reagent.

3. **Conclusion**: The cations that can be detected using `K4[Fe(CN)6]` are `Cu²⁺`, `Cd²⁺`, `Fe³⁺`, and `Zn²⁺`. The cation `Fe²⁺` cannot be detected.

### Final Answer:
The answer is that `K4[Fe(CN)6]` can be used to detect all cations except `Fe²⁺`.