Question

Which of the following elements does not have a completely filled outermost shell in its ground state?

• A. Neon
• B. Helium
• C. Oxygen
• D. Argon

Hint:

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).

Answer 1

The Correct Option is C

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.