Sugars are

Options

A. Optically active polyhydroxy aldehydes
B. Optically active polyhydroxy ketones
C. Optically active polyhydroxy aldehydes or ketones
D. polyhydroxy aldehydes or ketones which may or may not be optically active

Answer

**Step-by-Step Solution:**

1. **Understanding Sugars**: Sugars are classified as carbohydrates, and they can be categorized into different types based on their structure. The main types of sugars include monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

2. **Identifying Key Characteristics**: Sugars are characterized by the presence of multiple hydroxyl (-OH) groups and either an aldehyde group (-CHO) or a ketone group (C=O). This is crucial for their classification.

3. **Optical Activity**: Sugars are optically active due to the presence of at least one chiral carbon atom. A chiral carbon is a carbon atom that is attached to four different groups, leading to non-superimposable mirror images (enantiomers).

4. **Types of Sugars**: Based on the functional groups present:
- **Aldoses**: Sugars that contain an aldehyde group and are optically active polyhydroxy aldehydes.
- **Ketoses**: Sugars that contain a ketone group and are optically active polyhydroxy ketones.

5. **Conclusion**: Therefore, sugars can be defined as optically active polyhydroxy aldehydes and ketones. The correct option that encompasses this definition is that sugars are optically active polyhydroxy aldehydes and ketones.

**Final Answer**: Sugars are optically active polyhydroxy aldehydes and ketones.

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