Which is a non-reducing sugar?

Options

A. glucose
B. sucrose
C. galactose
D. mannose

Answer

To determine which is a non-reducing sugar among the given options, we can follow these steps:

### Step 1: Understand the Types of Sugars
- Sugars can be classified into two main categories: reducing sugars and non-reducing sugars.
- Reducing sugars have free aldehyde or ketone groups that can participate in redox reactions, while non-reducing sugars do not.

### Step 2: Identify the Options
- The options provided are:
1. Glucose (monosaccharide)
2. Sucrose (disaccharide)
3. Galactose (monosaccharide)
4. Mannose (monosaccharide)

### Step 3: Analyze Each Sugar
- **Glucose**: This is a monosaccharide with a free aldehyde group, making it a reducing sugar.
- **Galactose**: This is also a monosaccharide with a free aldehyde group, thus it is a reducing sugar.
- **Mannose**: Another monosaccharide with a free aldehyde group, hence it is a reducing sugar too.
- **Sucrose**: This is a disaccharide formed from glucose and fructose. In sucrose, the aldehyde group of glucose is involved in a glycosidic bond, which means it is not free to react. Therefore, sucrose does not reduce Tollens reagent or Fehling's solution.

### Step 4: Conclusion
- Since sucrose does not have a free aldehyde or ketone group, it is classified as a non-reducing sugar. Therefore, the correct answer is **option B: sucrose**.

### Summary of the Answer
The non-reducing sugar among the options provided is **sucrose**.

---