Electron configurations with one unpaired p electron

Steps:

• Determine atomic numbers: F(9), Ga(31), Ar(18), C(6), Ti(22), Se(34), Si(14).
• Write valence configurations: focus on p subshell (e.g., F: 2p⁵; Ga: 4p¹; Ar⁺: 3p⁵; C⁻: 2p³; Ti/Ti⁺: no valence p electrons; Se: 4p⁴; Si⁺: 3p¹).
• Apply Hund's rule: count unpaired p electrons (p⁵ or p¹ = 1 unpaired; p³ = 3; p⁴ = 2; full p⁶ = 0).
• Identify pair where both species have exactly one unpaired p electron.

Why C is correct:

• F (2p⁵) and Ga (4p¹) each have one unpaired electron in p subshell per Hund's rule.

Why the others are wrong:

• A: Ar⁺ has one unpaired p electron (3p⁵), but C⁻ has three (2p³).
• B: Neither Ti (3p⁶, full) nor Ti⁺ (3p⁶, full) has unpaired p electrons.
• D: Se has two unpaired p electrons (4p⁴), though Si⁺ has one (3p¹).

Final answer: C