Why do noble gases exist as monoatomic ?

Explanation

### Step-by-Step Solution

1. **Understanding Noble Gases**: Noble gases are elements found in Group 18 of the periodic table. They include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

2. **Electron Configuration**: The defining characteristic of noble gases is their electron configuration. They have a complete outer shell of electrons. For example, helium has 2 electrons, while neon has 8 electrons in its outer shell.

3. **Stability Due to Full Valence Shell**: Because their outer electron shells are fully filled, noble gases are very stable. This stability is a key reason why they do not readily react with other elements.

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