Question:medium
Which of the following elements does not have a completely filled outermost shell in its ground state?
Which of the following elements does not have a completely filled outermost shell in its ground state?
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Elements with a completely filled outermost shell are typically noble gases (except for elements like oxygen, which do not achieve this configuration in their ground state).
Updated On: Jan 13, 2026
- Neon
- Helium
- Oxygen
- Argon
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The Correct Option is C
Solution and Explanation
Ground state electron configurations and outermost shell completion for elements:
- Neon (Ne): 1s\(^2\) 2s\(^2\) 2p\(^6\) → Outermost shell has a complete octet.
- Helium (He): 1s\(^2\) → Outermost shell has a complete duet.
- Oxygen (O): 1s\(^2\) 2s\(^2\) 2p\(^4\) → The 2p orbital is not fully occupied (maximum capacity is 6 electrons).
- Argon (Ar): 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\) 3p\(^6\) → Outermost shell has a complete octet.
Answer: Oxygen lacks a completely filled outermost shell, making option (3) the correct choice.
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