In which of the following pairs are the ions isoelectronic ?
Mg$^{2+}$, Ar
Na$^{+}$, O$^{2-}$
Al$^{3+}$, Cl$^{-}$
K$^{+}$, Ne
Answer is Right!
Answer is Wrong!
This question was previously asked in
UPSC NDA-1 – 2019
– Mg²⁺: Magnesium (Mg) has atomic number 12, so it has 12 electrons. Mg²⁺ has lost 2 electrons, so it has 10 electrons.
– Ar: Argon (Ar) has atomic number 18, so it has 18 electrons.
– Na⁺: Sodium (Na) has atomic number 11, so it has 11 electrons. Na⁺ has lost 1 electron, so it has 10 electrons.
– O²⁻: Oxygen (O) has atomic number 8, so it has 8 electrons. O²⁻ has gained 2 electrons, so it has 10 electrons.
– Al³⁺: Aluminum (Al) has atomic number 13, so it has 13 electrons. Al³⁺ has lost 3 electrons, so it has 10 electrons.
– Cl⁻: Chlorine (Cl) has atomic number 17, so it has 17 electrons. Cl⁻ has gained 1 electron, so it has 18 electrons.
– K⁺: Potassium (K) has atomic number 19, so it has 19 electrons. K⁺ has lost 1 electron, so it has 18 electrons.
– Ne: Neon (Ne) has atomic number 10, so it has 10 electrons.
Comparing the pairs:
A) Mg²⁺ (10e⁻), Ar (18e⁻) – Not isoelectronic.
B) Na⁺ (10e⁻), O²⁻ (10e⁻) – Isoelectronic.
C) Al³⁺ (10e⁻), Cl⁻ (18e⁻) – Not isoelectronic.
D) K⁺ (18e⁻), Ne (10e⁻) – Not isoelectronic.