Which one among the following pairs is <strong>NOT</strong> correctly matched ?
- A. Nitrogen : Three unpaired electrons
- B. Carbon : Tetravalent
- C. Chlorine : Two stable isotopic forms
- D. Helium : Diatomic gas ✓
Correct Answer: D. Helium : Diatomic gas
Explanation
Helium is an inert, noble gas with a completely filled valence shell. Therefore, it exists as a monoatomic gas (He), not a diatomic gas.
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