Which one of the following is NOT correct for monosaccharides?
1. They are optically active polyhydroxy carbonyl compounds
2.Fructose is ketose sugar and hence it does not give red precipitate with Fehling solution
3. `alpha - D(+)` glucose and `beta - D(+)` glucose are anomers
4. Glucose and mannose are anomers

Options

A. 1,2
B. 2,3
C. 2,4
D. 1,2,3,4

Answer

To determine which statement is NOT correct for monosaccharides, we will analyze each option one by one.

### Step 1: Analyze Statement 1
**Statement 1:** "They are optically active polyhydroxy carbonyl compounds."

**Analysis:**
Monosaccharides are indeed optically active due to the presence of one or more chiral centers. They are also polyhydroxy compounds (having multiple hydroxyl groups) and contain a carbonyl group (either aldehyde or ketone). Therefore, this statement is **correct**.

### Step 2: Analyze Statement 2
**Statement 2:** "Fructose is a ketose sugar and hence it does not give a red precipitate with Fehling solution."

**Analysis:**
Fructose is a ketose sugar, but it can still reduce Fehling's solution, which is a test for reducing sugars. While it is true that fructose is a ketose, it can tautomerize to form an aldehyde under alkaline conditions, allowing it to give a positive test with Fehling's solution. Therefore, this statement is **incorrect**.

### Step 3: Analyze Statement 3
**Statement 3:** "Alpha-D(+) glucose and beta-D(+) glucose are anomers."

**Analysis:**
Alpha-D(+) glucose and beta-D(+) glucose differ in configuration at the anomeric carbon (C1) when they form their cyclic structures. This difference in configuration classifies them as anomers. Hence, this statement is **correct**.

### Step 4: Analyze Statement 4
**Statement 4:** "Glucose and mannose are anomers."

**Analysis:**
Glucose and mannose are not anomers; they are C2 epimers because they differ in configuration at the second carbon atom (C2). Anomers specifically refer to sugars that differ at the anomeric carbon (C1). Therefore, this statement is **incorrect**.

### Conclusion
Based on the analysis:
- Statement 1: Correct
- Statement 2: Incorrect
- Statement 3: Correct
- Statement 4: Incorrect

The question asks for the statement that is NOT correct for monosaccharides. The incorrect statements are 2 and 4.

Thus, the answer is **Option C: 2 and 4**.

---