Which of the following disaccharide is not a reducing sugar?

Options

A. (a) Glucose
B. (b) Lactose
C. (c) Maltose
D. (d) Sucrose

Answer

To determine which disaccharide is not a reducing sugar, we need to understand the characteristics of reducing and non-reducing sugars.

### Step-by-Step Solution:

1. **Understanding Reducing Sugars**:
- Reducing sugars are sugars that have a free aldehyde or ketone group. This allows them to act as reducing agents, meaning they can donate electrons to other molecules.
- Common tests to identify reducing sugars include the Benedict's test, where a color change indicates the presence of reducing sugars.

2. **Identifying Disaccharides**:
- The common disaccharides include sucrose, lactose, and maltose.
- Sucrose is composed of glucose and fructose, while lactose is made up of glucose and galactose, and maltose consists of two glucose units.

3. **Analyzing Sucrose**:
- Sucrose is formed by a glycosidic bond between glucose and fructose at the beta 1,2 position.
- In this structure, there is no free aldehyde or ketone group available, which means sucrose cannot act as a reducing sugar.

4. **Analyzing Lactose and Maltose**:
- Lactose and maltose both have free aldehyde or ketone groups.
- Therefore, they can reduce other substances and will show a positive result in the Benedict's test.

5. **Conclusion**:
- Since sucrose lacks a free aldehyde or ketone group and does not change color in the Benedict's test, it is classified as a non-reducing sugar.
- Thus, the answer to the question is **sucrose**.

### Final Answer:
The disaccharide that is not a reducing sugar is **sucrose**.

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