Which statement describes noble gases under standard conditions?

• A. They are inert because they have full outer shells.
• B. They have partially filled outer shells.
• C. They are highly reactive.
• D. They always form diatomic molecules.

Answer: (B)

Noble gases are stable because their outermost electron shell is complete. A full valence shell means they don’t need to gain, lose, or share electrons to be stable, so they don’t readily react with other elements under standard conditions. That makes them largely inert and typically monatomic in the gas phase, rather than forming bonds or diatomic molecules. If the outer shell were only partially filled, atoms would tend to interact and bond to achieve stability, which is not characteristic of noble gases in normal conditions.