A neutral Fluorine atom (F) has 9 electrons (atomic number = 9). The F⁻ ion has gained one electron, so it has $9 + 1 = 10$ electrons. Let's find the number of electrons for each option: A) O²⁻: Neutral Oxygen (O) has 8 electrons (atomic number = 8). O²⁻ has gained two electrons, so $8 + 2 = 10$ electrons. B) Na⁺: Neutral Sodium (Na) has 11 electrons (atomic number = 11). Na⁺ has lost one electron, so $11 - 1 = 10$ electrons. C) Ne: Neutral Neon (Ne) has 10 electrons (atomic number = 10). D) N⁻: Neutral Nitrogen (N) has 7 electrons (atomic number = 7). N⁻ has gained one electron, so $7 + 1 = 8$ electrons. Thus, N⁻ has 8 electrons, while F⁻ has 10 electrons. N⁻ is not isoelectronic with F⁻.
Which one of the following ions is not iso- electronic with F⁻ ?
Asked in UPSC NDA 2 2021 · Topic: Atomic Structure (Electronic Configurations of Multi-electron Atoms and Ions)
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