Cl$^{-}$ is not isoelectronic with
K$^{+}$
Mg$^{2+}$
S$^{2-}$
P$^{3-}$
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CDS-2 – 2022
– Mg$^{2+}$: Atomic number of Mg is 12. Mg$^{2+}$ has lost two electrons, so it has 12 – 2 = 10 electrons.
– S$^{2-}$: Atomic number of S is 16. S$^{2-}$ has gained two electrons, so it has 16 + 2 = 18 electrons.
– P$^{3-}$: Atomic number of P is 15. P$^{3-}$ has gained three electrons, so it has 15 + 3 = 18 electrons.
Thus, Cl$^{-}$ (18 electrons) is not isoelectronic with Mg$^{2+}$ (10 electrons).