Identify a monoatomic molecule.

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Accepted Answer

1. Definition: A monoatomic species consists of single atoms (no chemical bonds to other atoms).

2. Evaluate each option:
- (1) carbon monoxide: chemical formula $CO$ — two atoms (diatomic molecule).
- (2) Oxygen: elemental oxygen is $O_2$ — diatomic.
- (3) Helium: symbol $He$ — a noble gas that exists as single atoms (monoatomic).
- (4) Chlorine: elemental chlorine is $Cl_2$ — diatomic.

3. Only Helium is monoatomic.

FINAL_ANSWER: c

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