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 analyze the structures of the disaccharides provided and see if their reducing groups (aldehydic or ketonic) are involved in glycosidic bond formation.

### Step-by-Step Solution:

1. **Understanding Reducing and Non-Reducing Sugars**:
- Reducing sugars are those that have free aldehyde or ketone groups that can reduce other compounds. Non-reducing sugars do not have free reducing groups because they are involved in glycosidic bonds.

2. **Identifying the Disaccharides**:
- We need to look at the structures of the disaccharides provided in the options. Common disaccharides include sucrose, lactose, and maltose.

3. **Analyzing Sucrose**:
- Sucrose is composed of glucose and fructose. In sucrose, the glycosidic bond is formed between the anomeric carbon (C1) of glucose and the anomeric carbon (C2) of fructose. This means both reducing groups are involved in the bond formation, making sucrose a non-reducing sugar.

4. **Analyzing Other Disaccharides**:
- For other disaccharides like maltose and lactose, the reducing groups are not involved in the glycosidic bond formation. For instance:
- Maltose consists of two glucose units linked by a glycosidic bond between C1 of one glucose and C4 of another, leaving one reducing end free.
- Lactose consists of glucose and galactose, with a similar situation where one reducing end is free.

5. **Conclusion**:
- Since sucrose has both of its reducing groups involved in the glycosidic bond, it is classified as a non-reducing sugar. Therefore, the correct answer is **sucrose**.

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