Which one of the following ions is not iso-electronic with F⁻ ?
O²⁻
Na⁺
Ne
N⁻
Answer is Right!
Answer is Wrong!
This question was previously asked in
UPSC NDA-2 – 2021
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⁻.