The gas that is used for the treatment of cancer is

Analysis

The question asks for the specific noble gas that is utilized in medical applications, specifically for the treatment of cancer.

Concept Explanation

The noble gases (Group 18 elements) are generally inert, meaning they do not react easily. However, some of them have unique properties that make them useful in specialized fields:

• Neon: Primarily used in advertising signs and high-voltage indicators.
• Radon: This is a radioactive noble gas. Because it emits alpha particles, it can be used in radiotherapy to destroy cancerous cells. It is often used in the form of "seeds" implanted directly into or near a tumor to deliver localized radiation.
• Xenon: Used in specialized light sources, such as camera flashes and some high-intensity lamps.
• Argon: Used in light bulbs (to prevent the filament from burning) and in welding to provide an inert atmosphere.

Step-by-Step Solution

1. Identify the property required: The treatment of cancer (radiotherapy) requires a substance that is radioactive and can emit ionizing radiation to damage the DNA of cancer cells.
2. Evaluate the options: • Neon, Xenon, and Argon are stable noble gases and are not radioactive. • Radon ($^{222}\text{Rn}$) is the only radioactive noble gas among the choices.
3. Conclusion: Because Radon is radioactive, it is the only gas listed that is suitable for the medical treatment of cancer through radiotherapy.

Exam Tip

When dealing with noble gases in exams, remember their common uses:

• Helium: Balloons and deep-sea diving (mixed with oxygen).
• Neon: Signs/Lights.
• Argon: Inert atmosphere for welding/light bulbs.
• Radon: Radiotherapy (Cancer treatment).