QJEEAdv03Chf404: JEE Advanced 2003 Chemistry - Class 11 JEEAdv03Chf404 Solution: Which of the following pairs are isoelectronic and…

Isoelectronic species are those that have the same number of electrons. Isostructural species have the same geometric arrangement of atoms.

First, let's determine if the given pairs are isoelectronic.

• $NO_3^-$ : Nitrogen has 7 electrons, and each oxygen has 8 electrons. The negative charge adds one more electron. Therefore, $NO_3^-$ has $7 + 3 \cdot 8 + 1 = 32$ electrons.
• $CO_3^{2-}$ : Carbon has 6 electrons, each oxygen has 8 electrons, and the ${2-}$ charge adds 2 more electrons. Therefore, $CO_3^{2-}$ has $6 + 3 \cdot 8 + 2 = 32$ electrons.
• $ClO_3^-$ : Chlorine has 17 electrons, each oxygen has 8 electrons, and the negative charge adds 1 more electron. Therefore, $ClO_3^-$ has $17 + 3 \cdot 8 + 1 = 42$ electrons.
• $SO_3$ : Sulfur has 16 electrons, and each oxygen has 8 electrons. Therefore, $SO_3$ has $16 + 3 \cdot 8 = 40$ electrons.

Based on the number of electrons, $NO_3^-$ and $CO_3^{2-}$ are isoelectronic.

Now, let's determine if these species are isostructural. Both $NO_3^-$ and $CO_3^{2-}$ have a trigonal planar structure.

Therefore, the correct option is:

Option A: $NO_3^-$ , $CO_3^{2-}$