Correct Answer: Helium (He)
Subject: chemistry
Explanation: • <b>Key Fact</b> Helium is a monoatomic gas (exists as single atoms, He). • <b>Supporting Detail</b> Oxygen, Chlorine, and Hydrogen exist naturally as diatomic molecules (O₂, Cl₂, H₂). • <b>Related Concept</b> All noble gases (Group 18) are monoatomic due to complete valence shells. • <b>Why wrong options are wrong</b> Options B, C, and D are all diatomic elemental molecules. • <b>Exam Trick</b> Noble gases = Monoatomic (Single). • <b>Additional Info</b> Ozone (O₃) is an example of a triatomic molecule.
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