Final answer:
Noble gases can exist as single atoms because they have a complete valence electron shell. This full outer electron configuration makes them particularly stable and less likely to form bonds with other atoms.
Step-by-step explanation:
The molecules of a noble gas can exist as single atoms primarily because they have a complete valence electron shell, as option c) suggests. The noble gases—helium, neon, argon, etc.—have full outer electron configurations. This makes these elements particularly stable, exhibiting large ionization energies and low tendencies to accept additional electrons. Therefore, they do not readily form bonds to make molecules with other atoms. While noble gases do possess high ionization energy and have low electronegativity, as suggested in options a) and b), it is their complete valence electron shell that primarily contributes to their ability to exist as monatomic gases, as opposed to forming larger molecular structures.
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