Non-reducing sugar is

Options

A. maltose
B. sucrose
C. lactose
D. none of these.

Answer

To determine which of the given options is a non-reducing sugar, we need to understand the definition of non-reducing sugars and analyze each option accordingly.

### Step-by-step Solution:

1. **Understanding Non-reducing Sugars**:
Non-reducing sugars are carbohydrates that do not have a free aldehyde or ketone group. This means they cannot be oxidized and do not participate in reduction reactions, such as the Tollen's test or Benedict's test.

2. **Analyzing the Options**:
- **Option A: Maltose**: Maltose is a disaccharide composed of two glucose units. It has a free aldehyde group and can reduce Tollen's reagent, making it a reducing sugar.
- **Option B: Sucrose**: Sucrose is a disaccharide made up of glucose and fructose. It does not have a free aldehyde or ketone group because the glycosidic bond between glucose and fructose involves both anomeric carbons. Therefore, sucrose is a non-reducing sugar.
- **Option C: Lactose**: Lactose is a disaccharide made of glucose and galactose. It has a free aldehyde group and can reduce Tollen's reagent, making it a reducing sugar.
- **Option D: None of these**: This option suggests that none of the sugars listed are non-reducing, which is incorrect since sucrose is a non-reducing sugar.

3. **Conclusion**:
Based on the analysis, the only non-reducing sugar among the options provided is **sucrose**.

### Final Answer:
The correct answer is **Option B: Sucrose**.