in which of the following , the DNA is the principal constituent ?

Options

A. Nucleus
B. Chromatin
C. Ribosomes
D. Chloroplas

Answer

To solve the question "In which of the following, the DNA is the principal constituent?", we will analyze the options provided and determine where DNA is predominantly found.

### Step-by-Step Solution:

1. **Understanding DNA and its location**:
- DNA (Deoxyribonucleic acid) is the genetic material found in living organisms. In eukaryotic cells, DNA is primarily located in the nucleus.

2. **Analyzing the options**:
- **Option 1: Nucleus**:
- The nucleus is the membrane-bound organelle that contains the majority of the cell's genetic material in the form of chromatin (which is DNA wrapped around proteins). Therefore, DNA is indeed the principal constituent of the nucleus.
- **Option 2: Ribosomes**:
- Ribosomes are not primarily made of DNA. They are ribonucleoproteins, composed of ribosomal RNA (rRNA) and proteins. Hence, DNA is not a principal constituent here.
- **Option 3: Chloroplast**:
- Chloroplasts are organelles found in plant cells and some protists. They contain their own DNA, but the amount is significantly less than that found in the nucleus. Thus, while they have DNA, it is not the principal constituent.
- **Option 4: Chromatin**:
- Chromatin is a complex of DNA and proteins found in the nucleus. While it contains DNA, it is not an independent structure like the nucleus itself.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Nucleus**, as it is the organelle where DNA is the principal constituent.

### Final Answer:
**Nucleus**