Question

Which Of the following, isoelectronic & isostructural species are: $NO_3^ - ,ClO_3^ - ,SO_3^ - ,CO_3^{2 - }$
$
  (a).NO_3^ - andCO_3^{2 - } \\
  (b).SO_3^ - andCO_3^{2 - } \\
  (c).NO_3^ - andClO_3^ - \\
  (d).CO_3^{2 - }andClO_3^ - \\
 $

Answer 1

Hint: isoelectronic species are those having the same numbers of electrons or the same electronic structure while isostructural are those which have the same shape and hybridization.

Complete step by step answer:
We know that the number of electrons in a given compound is equal to the total number of electrons possessed by all the species in the compound.
So first we will add the number of electrons in the compounds
Nitrogen, oxygen, carbon, sulphur and chlorine have 7, 8, 6, 16 and 17 electrons respectively.
The number of negative charges on each compound indicates the number of extra electrons present in the compound.
$
  NO_3^ - = 32e \\
  CO_3^{2 - } = 32e \\
  SO_3^ - = 41e \\
  ClO_3^ - = 42e \\
 $
Therefore, $NO_3^ - $ and​ $CO_3^{2 - }$ are isoelectronic because the total no. of electrons in the compounds are equal.
The structures of both $NO_3^ - $ and​ $CO_3^{2 - }$ are trigonal planar because they both have same hybridisation $s{p^3}$ and the same number of oxygen atoms is surrounded with the central atom.
Therefore $NO_3^ - $ and​ $CO_3^{2 - }$ are isostructural also.

So, the correct option is A.

Note:
Isobars species are the species which have the same atomic mass while isotopic species are the species which have the same atomic number. Isobars have the same physical properties but differ in chemical properties. Isotopes have the same physical and chemical properties.