Common radioactive elements present in human body are

Options

A. Carbon-14
B. N-15
C. K-40
D. Both A and C.

Answer

### Step-by-Step Solution:

1. **Understanding Radioactive Elements**:
- Radioactive elements are those that contain unstable nuclei and release radiation as they decay to become more stable.

2. **Common Radioactive Elements in the Human Body**:
- The human body contains certain naturally occurring radioactive elements. The most common ones include:
- **Carbon-14 (C-14)**: This isotope of carbon is produced in the atmosphere and is incorporated into living organisms through the food chain.
- **Potassium-40 (K-40)**: This isotope of potassium is naturally present in the earth's crust and is absorbed by the human body through food and water.
- **Radium-226 (Ra-226)**: Although less common, radium can also be found in trace amounts in the human body.

3. **Sources of Radioactive Elements**:
- Humans are exposed to these radioactive elements from various sources:
- **Natural Sources**: These include soil, rocks, and cosmic rays.
- **Dietary Sources**: Foods and water can contain trace amounts of these radioactive elements.

4. **Conclusion**:
- Based on the information, the common radioactive elements present in the human body are Carbon-14 and Potassium-40. Therefore, the correct answer to the question is **both A (Carbon-14) and C (Potassium-40)**.

### Final Answer:
The common radioactive elements present in the human body are Carbon-14 and Potassium-40.

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