Which one of the following is not correct ?

Options

A. D(-) Fructose exists in furanose structure
B. D(+) Glucose exists in pyranose structure.
C. In sucrose the two monosaccharides are held together by peptide linkage
D. Maltose is a reducing sugar.

Explanation

To determine which statement is not correct, let's analyze each option step by step.

### Step 1: Analyze the first statement
**Statement:** D minus fructose exists in Furanose structure.

- **Explanation:** D minus fructose can indeed exist in a Furanose structure, which is a five-membered ring. This is a correct statement.

### Step 2: Analyze the second statement
**Statement:** D plus glucose exists in pyranose structure.

- **Explanation:** D plus glucose can form a six-membered ring structure known as the Pyranose structure. This is also a correct statement.

### Step 3: Analyze the third statement
**Statement:** In sucrose, the two monosaccharides are held together by peptide linkage.

- **Explanation:** Sucrose is a disaccharide formed from glucose and fructose. The two monosaccharides are linked together by a glycosidic linkage, not a peptide linkage. Therefore, this statement is incorrect.

### Step 4: Analyze the fourth statement
**Statement:** Maltose is a reducing sugar.

- **Explanation:** Maltose is indeed a reducing sugar because it has a free aldehyde group that can reduce other compounds. This is a correct statement.

### Conclusion
After analyzing all the statements:
- The first statement is correct.
- The second statement is correct.
- The third statement is incorrect (as it mentions peptide linkage instead of glycosidic linkage).
- The fourth statement is correct.

Thus, the statement that is not correct is the third one: "In sucrose, the two monosaccharides are held together by peptide linkage."

### Final Answer
**The incorrect statement is:** In sucrose, the two monosaccharides are held together by peptide linkage.

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