Which one of the following is not a part of the nucleus?

Options

A. A. Ribosome
B. B. Nucleolus
C. C. Chromosome
D. D. Gene

Explanation

To determine which option is not a part of the nucleus, let's analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Understanding the Nucleus**:
- The nucleus is a membrane-bound organelle found in eukaryotic cells. It contains the cell's genetic material (DNA) and is responsible for controlling the cell's growth, metabolism, and reproduction.

2. **Analyzing the Options**:
- **Option 1: Ribosome**:
- Ribosomes are small structures that synthesize proteins. They are not found within the nucleus; instead, they are located in the cytoplasm or on the rough endoplasmic reticulum. Thus, ribosomes are not a part of the nucleus.

- **Option 2: Nucleus**:
- This option is self-referential and cannot be considered as a part of itself. The nucleus is the organelle in question.

- **Option 3: Chromosome**:
- Chromosomes are structures within the nucleus that contain DNA. They are indeed a part of the nucleus.

- **Option 4: Gene**:
- Genes are segments of DNA located on chromosomes. Since chromosomes are part of the nucleus, genes are also considered part of the nucleus.

3. **Conclusion**:
- After analyzing all the options, it is clear that ribosomes are not a part of the nucleus, while chromosomes and genes are integral components of it. Therefore, the correct answer is **Ribosome**.

### Final Answer:
**Ribosome** is not a part of the nucleus.