Helium is an unreactive gas and neon has very poor reactivity. What do these elements have in common?

Explanation

**Step-by-Step Solution:**

1. **Identify the Elements**: The question mentions two elements: Helium (He) and Neon (Ne).

2. **Classify the Elements**: Both Helium and Neon belong to a specific group in the periodic table known as the noble gases or inert gases.

3. **Understand the Electronic Configuration**: Noble gases have a complete outer electron shell. For Helium, the electronic configuration is 1s², and for Neon, it is 1s² 2s² 2p⁶. This complete outer shell contributes to their stability.

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