Which of the following isotpes is most dangerous to human beings ?

Options

A. Phosphorus-32
B. Strontium-90
C. Caesium -137
D. Iodine-131

Explanation

To determine which isotope is most dangerous to human beings, we will analyze each of the given isotopes based on their properties and effects on human health.

### Step-by-Step Solution:

1. **Identify the Isotopes**: The isotopes provided are:
- Phosphorus-32 (P-32)
- Strontium-90 (Sr-90)
- Cesium-133 (Cs-133)
- Cesium-137 (Cs-137)
- Iodine-131 (I-131)

2. **Understand Radioactivity**: Recognize that some isotopes are radioactive and can emit harmful radiation, which can damage human cells and DNA.

3. **Evaluate Each Isotope**:
- **Phosphorus-32 (P-32)**: Used in medical applications, it has a relatively short half-life and is less harmful compared to others.
- **Strontium-90 (Sr-90)**: A byproduct of nuclear fission, it is highly radioactive and can accumulate in bones.
- **Cesium-133 (Cs-133)**: Primarily used in atomic clocks, it is stable and not considered dangerous.
- **Cesium-137 (Cs-137)**: Also radioactive, but less harmful than Sr-90 when considering long-term effects.
- **Iodine-131 (I-131)**: Used in medical treatments, particularly for thyroid conditions, but has a shorter half-life and less potential for long-term harm.

4. **Determine the Most Dangerous Isotope**:
- Among the isotopes, **Strontium-90 (Sr-90)** is the most dangerous due to its ability to accumulate in bones and bone marrow, leading to severe health issues such as bone cancer and leukemia.

5. **Conclusion**: The most dangerous isotope to human beings from the list provided is **Strontium-90 (Sr-90)**.

### Final Answer:
**Strontium-90 (Sr-90)** is the most dangerous isotope to human beings.

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