Which of the following noble gases cannot be used for filling up electric bulbs?

Options

A. helium
B. neon
C. argon
D. radon

Explanation

To solve the question, "Which of the following noble gases cannot be used for filling up electric bulbs?" we will analyze each option provided and determine which noble gas is unsuitable for this purpose.

### Step-by-Step Solution:

1. **Understand the Purpose of Noble Gases in Electric Bulbs**:
- Noble gases are used in electric bulbs to prevent the tungsten filament from sublimating. Sublimation is the process where a solid turns directly into a gas. Noble gases do not react with tungsten or other components in the bulb, making them ideal for this purpose.

2. **Evaluate Each Noble Gas Option**:
- **Option 1: Helium**:
- Helium can be used in electric bulbs, although it is not commonly used. Therefore, it is not the answer.
- **Option 2: Neon**:
- Neon can also be used in electric bulbs. Similar to helium, it is not the answer.
- **Option 3: Argon**:
- Argon is the most commonly used noble gas in electric bulbs. It effectively slows down the sublimation of tungsten. Thus, this option is not the answer.
- **Option 4: Radon**:
- Radon is a radioactive noble gas. Due to its radioactivity, it is not safe for use in electric bulbs. Therefore, radon is the correct answer.

3. **Conclusion**:
- The noble gas that cannot be used for filling up electric bulbs is **Radon**.

### Final Answer:
**Radon**