Which of the following pairs of monosaccharides will form the same osazone

Options

A. D-glucose and L-glucose
B. D-glucose and D-galactose
C. D-glucose and D-fructose
D. D-glucose and D-allose

Answer

To determine which pairs of monosaccharides will form the same osazone, we need to analyze the structures of the given monosaccharides and their corresponding osazones. The key point is that the osazone formation involves the reaction of the carbonyl group (aldehyde or ketone) and the hydroxyl groups of the monosaccharides.

### Step-by-Step Solution:

1. **Identify the Monosaccharides**: The options provided include D-Glucose, L-Glucose, D-Galactose, D-Fructose, and D-Allose.

2. **Draw the Structure of D-Glucose**:
- D-Glucose is an aldohexose with the following structure:
```
CHO
|
H-C-OH
|
HO-C-H
|
H-C-OH
|
CH2OH
```

3. **Determine the Osazone Formation**:
- When D-Glucose reacts with phenylhydrazine, it forms glucose osazone. The reaction involves the carbonyl group at C1 and the hydroxyl group at C2.

4. **Analyze Other Monosaccharides**:
- **L-Glucose**: The structure is similar to D-Glucose but with the configuration at C2 reversed. The last four carbons do not match D-Glucose, so it will not form the same osazone.
- **D-Galactose**: The configuration at C4 is different from D-Glucose. Thus, it will not form the same osazone.
- **D-Fructose**: This is a ketose, and its structure is:
```
CH2OH
|
C=O
|
H-C-OH
|
H-C-OH
|
H-C-OH
```
The last four carbons (C2 to C5) have the same substituent arrangement as D-Glucose, which means it will form the same osazone.
- **D-Allose**: The configuration of the hydroxyl groups is different from D-Glucose, so it will not form the same osazone.

5. **Conclusion**: The pair of monosaccharides that will form the same osazone as D-Glucose is D-Fructose.

### Final Answer:
The correct answer is **D-Glucose and D-Fructose** will form the same osazone.