The structural unit of bone is

Options

A. Chondrin
B. Cyton
C. Osteon
D. Ossein.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the structural unit of bone. We need to evaluate the given options to identify which one correctly represents this unit.

2. **Evaluating Option 1: Chondrine**:
- Chondrine is described as a bluish-white gelatin-like substance, a carbohydrate-protein complex obtained by boiling cartilage in water.
- **Conclusion**: This is related to cartilage, not bone. Therefore, this option is incorrect.

3. **Evaluating Option 2: Cyton**:
- A cyton is the cell body of a neuron, which is part of the nervous system.
- **Conclusion**: Since it pertains to nerve cells and not bone, this option is also incorrect.

4. **Evaluating Option 3: Osteon**:
- Osteon is defined as the functional and structural unit of compact bone. It is also known as the Haversian system.
- **Details**: The osteon consists of concentric layers of compact bone tissue surrounding a central canal (Haversian canal) that contains blood vessels and nerves.
- **Conclusion**: This option is correct as it directly relates to the structure of bone.

5. **Evaluating Option 4: O-A-C-E-N**:
- O-A-C-E-N refers to a protein that is the organic extracellular matrix of bone, primarily made of collagen.
- **Conclusion**: While it is important for the structure of bone, it is not the structural unit itself. Thus, this option is incorrect.

6. **Final Answer**: After evaluating all options, the structural unit of bone is **osteon**.