Carbohydrates are commonly defined as:

Options

A. Polycarbonyi compounds
B. Polycarboxylic acid
C. Polyhydroxy carboxylic acid
D. Polyhydroxy aldehyde and ketone

Explanation

**Step-by-Step Solution:**

1. **Understanding Carbohydrates**: Carbohydrates are organic compounds that are essential for various biological functions. They are primarily composed of carbon (C), hydrogen (H), and oxygen (O).

2. **Definition of Carbohydrates**: Carbohydrates are commonly defined as optically active polyhydroxyaldehydes or polyhydroxyketones. This means they contain multiple hydroxyl (-OH) groups and either an aldehyde group (-CHO) or a ketone group (C=O).

3. **Types of Carbohydrates**:
- **Aldoses**: These are carbohydrates that contain an aldehyde group. An example is glucose, which has the structure that includes a CHO group.
- **Ketoses**: These are carbohydrates that contain a ketone group. An example is fructose, which has a C=O group.

4. **Structure of Glucose**: Glucose is an aldose. Its structure can be represented as:
- C6H12O6 (with multiple -OH groups and one -CHO group).
- This confirms that glucose fits the definition of a polyhydroxyaldehyde.

5. **Structure of Fructose**: Fructose is a ketose. Its structure can be represented as:
- C6H12O6 (with multiple -OH groups and one C=O group).
- This confirms that fructose fits the definition of a polyhydroxyketone.

6. **Conclusion**: Therefore, carbohydrates are defined as optically active polyhydroxyaldehydes or polyhydroxyketones, and they do not contain carboxylic groups or are not classified as carbonyl compounds.

**Final Answer**: Carbohydrates are commonly defined as optically active polyhydroxyaldehydes or polyhydroxyketones.

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