In disaccharides, if the reducing groups of monosaccharides, i.e., aldehydic or ketonic groups are bonded, these are non-reducing sugars. Which of the following disaccharide is a non-reducing sugar?

Options

A.
B.
C.
D.

Explanation

To determine which disaccharide is a non-reducing sugar, we need to understand the concept of reducing and non-reducing sugars based on the presence of free aldehydic or ketonic groups in the monosaccharides that make up the disaccharide.

### Step-by-Step Solution:

1. **Understanding Reducing and Non-Reducing Sugars**:
- Reducing sugars are those that have a free aldehyde or ketone group. This allows them to reduce other compounds and participate in redox reactions.
- Non-reducing sugars do not have a free aldehyde or ketone group because the reducing groups are involved in glycosidic bonds.

2. **Identifying the Anomeric Carbon**:
- In a disaccharide, each monosaccharide has an anomeric carbon, which is the carbon derived from the carbonyl carbon of the monosaccharide.
- If the anomeric carbon of either monosaccharide is involved in a glycosidic bond (i.e., it is bonded to another monosaccharide), it cannot act as a reducing sugar.

3. **Analyzing the Given Disaccharides**:
- We need to look at the structure of the disaccharides provided in the options and identify the anomeric carbons.
- If both anomeric carbons are involved in glycosidic bonds and do not have a free hydroxyl (OH) group, then the disaccharide is non-reducing.

4. **Conclusion**:
- After analyzing the structures, we find that the disaccharide that has both anomeric carbons involved in glycosidic bonds, without any free OH group, is classified as a non-reducing sugar.
- For example, sucrose is a common non-reducing sugar because both of its anomeric carbons are involved in the glycosidic bond, leaving no free OH group.

### Final Answer:
The disaccharide that is a non-reducing sugar is **sucrose**.