Which of the following cannot distinguish between glucose and fructose ?

Options

A. Tollen's reagent
B. Fehling solution
C. Benedict's solution
D. All of these.

Explanation

To determine which of the following cannot distinguish between glucose and fructose, we need to analyze the properties of each reagent mentioned: Tollens reagent, Fehling's solution, and Benedict's solution.

### Step-by-Step Solution:

1. **Understanding Glucose and Fructose**:
- Glucose is an aldohexose, meaning it contains an aldehyde group (-CHO) and has the formula C₆H₁₂O₆.
- Fructose is a ketohexose, meaning it contains a ketone group (C=O) and also has the same formula C₆H₁₂O₆.

2. **Identifying the Reagents**:
- **Tollens Reagent**: This reagent is used to detect aldehydes. It can oxidize glucose (which has an aldehyde group) to form gluconic acid, producing a silver mirror. However, fructose can also give a positive result after rearrangement to glucose under certain conditions.
- **Fehling's Solution**: This solution is also used to test for aldehydes. Glucose will reduce the copper(II) ions in Fehling's solution to form a red precipitate of copper(I) oxide. Fructose can also give a positive result after rearrangement to glucose.
- **Benedict's Solution**: Similar to Fehling's solution, Benedict's solution can also detect reducing sugars. Both glucose and fructose will react positively.

3. **Conclusion**:
- All three reagents (Tollens, Fehling's, and Benedict's) can react with both glucose and fructose, either directly or through rearrangement.
- Therefore, none of these reagents can distinctly identify glucose from fructose.

4. **Final Answer**: The answer is that **none of the reagents (Tollens reagent, Fehling's solution, and Benedict's solution) can distinguish between glucose and fructose**.