Hepatitis B is caused by:

Options

A. RNA virus
B. DNA virus
C. Mycoplasma
D. Rickettsia

Answer

### Step-by-Step Solution:

1. **Understanding Hepatitis B**:
- Hepatitis B is primarily a liver disease. It is important to know what causes this disease to understand its implications on human health.

2. **Identifying the Causative Agent**:
- The causative agent of Hepatitis B is a virus known as the Hepatitis B virus (HBV).

3. **Classifying the Virus**:
- HBV belongs to a specific genus called Orthohepadnavirus and is part of the family Hepadnaviridae.

4. **Determining the Type of Virus**:
- It is crucial to identify whether HBV is an RNA virus or a DNA virus. In this case, Hepatitis B virus is classified as a DNA virus.

5. **Analyzing the Options**:
- The options provided are:
1. RNA virus
2. DNA virus
3. Mycoplasma
4. Rickettsia
- Based on our understanding, we can eliminate the first option (RNA virus) because HBV is a DNA virus.

6. **Final Conclusion**:
- The correct answer is option 2: Hepatitis B is caused by a DNA virus.