Reducing sugars are characterised by the presence of free

Options

A. Aldehyde or Keto group
B. Aldehyde and Keto group
C. Keto group only
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding Reducing Sugars**: Reducing sugars are carbohydrates that can act as reducing agents. This means they can donate electrons to other molecules.

2. **Key Characteristic**: The defining feature of reducing sugars is the presence of a free functional group that can participate in redox reactions. This functional group can either be an aldehyde group or a ketone group.

3. **Types of Groups**:
- **Aldehyde Group**: This is a carbonyl group (C=O) located at the end of a carbon chain. Sugars with this group are known as aldoses.
- **Ketone Group**: This is a carbonyl group located within the carbon chain. Sugars with this group are known as ketoses.

4. **Examples of Reducing Sugars**:
- All monosaccharides (like glucose and fructose) are reducing sugars because they have either a free aldehyde or ketone group.
- Some disaccharides (like lactose and maltose) can also be reducing sugars if they have a free anomeric carbon.

5. **Testing for Reducing Sugars**: Reducing sugars can be identified using Benedict's solution, which will produce a red precipitate when a reducing sugar is present.

6. **Conclusion**: Based on the characteristics of reducing sugars, the correct answer to the question is that they are characterized by the presence of free aldehyde or ketone groups.

**Final Answer**: Reducing sugars are characterized by the presence of free aldehyde or ketone groups.

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