A : Glucose, Mannose and Fructose form identical osazone.
R : Glucose, Mannose and Fructose have identical configuration at 3rd, 4th and 5th carbon atom

Options

A. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements, then mark (4).

Answer

To solve the assertion and reason question regarding glucose, mannose, and fructose forming identical osazones, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Understanding the Assertion (A)
The assertion states that glucose, mannose, and fructose form identical osazones.

- **Osazone Formation**: Osazones are formed when sugars react with phenylhydrazine. This reaction occurs at the carbonyl group (C=O) of the sugar.
- **Identical Osazones**: If the osazones formed from glucose, mannose, and fructose are identical, it means that the structure of the osazones is the same, indicating that the sugars must have similar configurations at the reactive sites.

### Step 2: Analyzing the Structures of the Sugars
1. **Glucose**: An aldose with the structure:
- C1: CHO (aldehyde)
- C2: CH2OH
- C3: CHOH (OH on the right)
- C4: CHOH (OH on the right)
- C5: CH2OH

2. **Mannose**: An aldose similar to glucose but with a different configuration at C2:
- C1: CHO (aldehyde)
- C2: CH2OH (OH on the left)
- C3: CHOH (OH on the right)
- C4: CHOH (OH on the right)
- C5: CH2OH

3. **Fructose**: A ketose with the structure:
- C1: CH2OH
- C2: C=O (ketone)
- C3: CHOH (OH on the left)
- C4: CHOH (OH on the right)
- C5: CH2OH

### Step 3: Identifying the Reactive Carbon Atoms
- The formation of osazones occurs primarily at the first two carbon atoms (C1 and C2) of the sugars.
- The configuration of the remaining carbon atoms (C3, C4, C5) is crucial in determining whether the osazones will be identical.

### Step 4: Analyzing the Reason (R)
The reason states that glucose, mannose, and fructose have identical configurations at the 3rd, 4th, and 5th carbon atoms.

- **Identical Configuration**:
- For glucose and mannose, the configurations at C3, C4, and C5 are indeed identical.
- For fructose, although it has a different structure (being a ketose), the configurations at C3, C4, and C5 are also similar to those in glucose and mannose.

### Conclusion
- Since all three sugars (glucose, mannose, and fructose) have the same configuration at C3, C4, and C5, they will form identical osazones when reacted with phenylhydrazine.
- Therefore, both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion.

### Final Answer
Both A and R are true, and R is the correct explanation of A.