Which does not represent a concentration cell?

Options

A. `Pt|H_(2)|HCl||HCl|Pt|H_(2)`
B. `Pt|H_(2)|HCl||Cl_(2)|Pt`
C. `Zn|Zn^(2+)||Cu^(2+)|Cu`
D. `Fe|Fe^(+2)||Cu^(2+)|Cu`

Explanation

To determine which option does not represent a concentration cell, we need to understand the characteristics of a concentration cell. A concentration cell is defined by having two half-cells that involve the same species but at different concentrations, and the reactions in the two half-cells are essentially reverse of each other. This means that the standard cell potential (E°) for a concentration cell is zero.

### Step-by-Step Solution:

1. **Understanding Concentration Cells**:
- A concentration cell has two electrodes made of the same material but immersed in solutions of different concentrations. The reactions in the two compartments are opposite, leading to E° = 0.

2. **Analyzing Option A**:
- **Reactions**:
- Cathodic reaction: \(2H^+ + 2e^- \rightarrow H_2\)
- Anodic reaction: \(H_2 \rightarrow 2H^+ + 2e^-\)
- **Conclusion**: The reactions are opposite, so this is a concentration cell.

3. **Analyzing Option B**:
- **Reactions**:
- Cathodic reaction: \(Cl_2 + 2e^- \rightarrow 2Cl^-\)
- Anodic reaction: \(H_2 \rightarrow 2H^+ + 2e^-\)
- **Conclusion**: The reactions are not reverse of each other, so this does not represent a concentration cell.

4. **Analyzing Option C**:
- **Reactions**:
- Cathodic reaction: \(Cu^{2+} + 2e^- \rightarrow Cu\)
- Anodic reaction: \(Zn \rightarrow Zn^{2+} + 2e^-\)
- **Conclusion**: The reactions are not reverse of each other, so this does not represent a concentration cell.

5. **Analyzing Option D**:
- **Reactions**:
- Cathodic reaction: \(Cu^{2+} + 2e^- \rightarrow Cu\)
- Anodic reaction: \(Fe \rightarrow Fe^{2+} + 2e^-\)
- **Conclusion**: The reactions are not reverse of each other, so this does not represent a concentration cell.

### Final Answer:
The options that do not represent a concentration cell are **B, C, and D**.