In electrolyte concentration cell:

Options

A. the electrode material and the solution in both half-cells are composed of the same substances
B. only the concentrations of solutions of ther same substances is different
C. `E_(cell)^(@)=0`
D. the Nernst equations reduces to `E_(cell)=-((0.0591)/(n))` log Q at `25^(@)C`

Answer

To solve the question regarding the electrolyte concentration cell, we will analyze each of the four options provided and determine their validity step by step.

### Step-by-Step Solution:

1. **Understanding the Electrolyte Concentration Cell**:
- An electrolyte concentration cell consists of two half-cells that contain the same electrode material but different concentrations of the same electrolyte solution. For example, both half-cells could use copper (Cu) electrodes immersed in copper sulfate (CuSO4) solutions of different concentrations.

2. **Analyzing Option A**:
- **Statement**: "The electrode material and the solution in both half-cells are composed of the same substances."
- **Evaluation**: This statement is true because, in an electrolyte concentration cell, both half-cells use the same electrode material (e.g., Cu) and the same electrolyte (e.g., CuSO4).
- **Conclusion**: Option A is correct.

3. **Analyzing Option B**:
- **Statement**: "Only the concentrations of the solution of the same substance is different."
- **Evaluation**: This statement is also true. The key feature of an electrolyte concentration cell is that while the electrode materials are the same, the concentrations of the electrolytic solutions differ, creating a potential difference.
- **Conclusion**: Option B is correct.

4. **Analyzing Option C**:
- **Statement**: "E_cell = E°_cell = 0."
- **Evaluation**: This statement is true. Since both half-cells consist of the same material, the standard cell potential (E°_cell) is zero. The potential difference arises solely due to the concentration difference.
- **Conclusion**: Option C is correct.

5. **Analyzing Option D**:
- **Statement**: "The Nernst equation reduces to E_cell = -0.0591/n * log Q."
- **Evaluation**: The Nernst equation is given by E_cell = E°_cell - (0.0591/n) * log Q. Since E°_cell = 0 for this cell, the equation simplifies to E_cell = - (0.0591/n) * log Q, which is consistent with the statement provided.
- **Conclusion**: Option D is correct.

### Final Conclusion:
All four options (A, B, C, and D) are correct regarding the characteristics of an electrolyte concentration cell.