Benedict's solution and Fehling's solution are similar in all of the following except:

Options

A. Both consist of a solultion of `CuSO_(4)`.
B. Both contain NaOH and complexing reagent.
C. Both contain `Cu^(2+)` ion as the oxidising agent.
D. Sodium citrate is used in Benedict's solution and Rochelle salt in Fehling's solution.

Answer

To solve the question regarding the similarities and differences between Benedict's solution and Fehling's solution, we will analyze each statement provided in the options.

### Step-by-Step Solution:

1. **Understanding the Purpose of the Solutions**:
- Both Benedict's solution and Fehling's solution are used to test for the presence of aldehyde groups in organic compounds. This is a common characteristic of both solutions.

2. **Analyzing the Components**:
- **Statement A**: Both contain copper sulfate.
- **Explanation**: This statement is true. Both solutions contain copper(II) sulfate (CuSO₄), which is essential for the redox reaction that occurs when testing for aldehydes.

3. **Basic Medium Requirement**:
- **Statement B**: Both contain sodium hydroxide and a complexing reagent.
- **Explanation**: This statement is also true. Both solutions require a basic medium (sodium hydroxide, NaOH) to facilitate the reaction and form complexes with the copper ions.

4. **Oxidizing Agent**:
- **Statement C**: Both contain Cu²⁺ ions as the oxidizing agent.
- **Explanation**: This statement is correct. In both solutions, Cu²⁺ ions act as the oxidizing agent, which is reduced to Cu⁺ (cuprous) ions during the reaction with aldehydes.

5. **Different Complexing Agents**:
- **Statement D**: Sodium citrate is used in Benedict's solution and Rochelle salt is used in Fehling's solution.
- **Explanation**: This statement is true and highlights a difference between the two solutions. Sodium citrate is indeed used in Benedict's solution, while Rochelle salt (potassium sodium tartrate) is used in Fehling's solution. This is the exception that distinguishes the two solutions.

### Conclusion:
The correct answer to the question is **Statement D**, as it indicates a difference between Benedict's solution and Fehling's solution.