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

The electron configuration of each element in its ground state: - Neon (Ne): 1s\(^2\) 2s\(^2\) 2p\(^6\) → Complete octet in the outermost shell. - Helium (He): 1s\(^2\) → Complete duet in the outermost shell. - Oxygen (O): 1s\(^2\) 2s\(^2\) 2p\(^4\) → Not completely filled in the 2p orbital (can hold 6 electrons). - Argon (Ar): 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\) 3p\(^6\) → Complete octet in the outermost shell. Answer: Oxygen does not have a completely filled outermost shell, so the correct answer is option (3).