The substance used in cancer therapy is

Options

A. Rn
B. Ni
C. Fe
D. Co

Explanation

To solve the question regarding the substance used in cancer therapy, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Question**: The question asks for the substance used in cancer therapy from the provided options.

2. **Review the Options**: The options given are:
- Option 1: Radon
- Option 2: Nickel
- Option 3: Iron
- Option 4: Cobalt

3. **Understand Cancer Therapy**: Cancer therapy often involves the use of certain isotopes or elements that can target cancer cells. One common method is radiation therapy, which utilizes radioactive isotopes.

4. **Evaluate Each Option**:
- **Radon**: This is a radioactive noble gas, but it is not commonly used in cancer therapy.
- **Nickel**: While nickel has various industrial applications, it is not typically associated with cancer treatment.
- **Iron**: Iron is essential for various biological functions but is not used in cancer therapy.
- **Cobalt**: Cobalt, specifically the isotope Cobalt-60, is widely used in radiation therapy for cancer treatment.

5. **Select the Correct Answer**: Based on the evaluation, the correct answer is **Cobalt** (Option 4), as it is used in cancer therapy.

### Final Answer:
The substance used in cancer therapy is **Cobalt**.

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