Which of the following statements are correct?

Options

A. Monosaccharides are optically active polyhydroxy carbonyl compounds.
B. Fructose does not react with Fehling's solution because it is keto.
C. `alpha`-D-Glucose and `beta`-D-Glucose are anomers.
D. D-Glucose and D-Mannose are epimers.

Answer

To determine which statements are correct, let's analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** Monosaccharides are optically active polyhydroxycarbonyl compounds.

**Analysis:**
- Monosaccharides are indeed the simplest carbohydrates and contain multiple hydroxyl (–OH) groups and either an aldehyde (CHO) or a ketone (C=O) group.
- The presence of one or more chiral carbon atoms in monosaccharides makes them optically active.
- Therefore, this statement is **correct**.

### Step 2: Analyze the Second Statement
**Statement:** Fructose doesn't react with the Fehling's solution because it’s a keto.

**Analysis:**
- Fructose is a reducing sugar, which means it can reduce Fehling's solution and Tollens' reagent.
- Even though fructose has a ketone group, it can tautomerize to form an aldehyde under alkaline conditions, allowing it to react with Fehling's solution.
- Therefore, this statement is **incorrect**.

### Step 3: Analyze the Third Statement
**Statement:** Alpha D-glucose and beta D-glucose are anomers.

**Analysis:**
- Anomers are a specific type of stereoisomer that differ at the anomeric carbon (C1) in cyclic forms of sugars.
- Alpha D-glucose has the hydroxyl group on the anomeric carbon (C1) in the opposite position to that of beta D-glucose.
- Therefore, this statement is **correct**.

### Step 4: Analyze the Fourth Statement
**Statement:** D-glucose and D-mannose are epimers.

**Analysis:**
- Epimers are diastereomers that differ at only one specific carbon atom.
- D-glucose and D-mannose differ at the second carbon (C2) in their structure.
- Therefore, this statement is **correct**.

### Conclusion
The correct statements are:
1. Monosaccharides are optically active polyhydroxycarbonyl compounds. (Correct)
2. Fructose doesn't react with the Fehling's solution because it’s a keto. (Incorrect)
3. Alpha D-glucose and beta D-glucose are anomers. (Correct)
4. D-glucose and D-mannose are epimers. (Correct)

Thus, the correct statements are **1, 3, and 4**.

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