To determine which pairs of ions are isoelectronic and isostructural, we need to analyze the number of electrons and the geometry of each ion.

Concept:

• Isoelectronic species have the same number of electrons.
• Isostructural species have the same shape/geometry. The geometry is determined by the hybridization of the central atom and the number of lone pairs.

Why (D) is correct:

Let's analyze option (D) ${\mathrm{ClO}}_3^{-}$ and ${\mathrm{SO}}_3^{2-}$:

• Number of electrons:
  For ${\mathrm{ClO}}_3^{-}$: Electrons = 17 (Cl) + 3 * 8 (O) + 1 (charge) = 17 + 24 + 1 = 42 electrons.
  For ${\mathrm{SO}}_3^{2-}$: Electrons = 16 (S) + 3 * 8 (O) + 2 (charge) = 16 + 24 + 2 = 42 electrons.
  Both ions have 42 electrons, so they are isoelectronic.
• Structure/Geometry:
  For ${\mathrm{ClO}}_3^{-}$: Central atom is Cl. Valence electrons = 7. Three oxygen atoms form single bonds (or double bonds, but for VSEPR, we count electron domains). One lone pair on Cl. Total electron domains = 3 (bond pairs) + 1 (lone pair) = 4. This corresponds to sp3 hybridization and a trigonal pyramidal geometry.
  For ${\mathrm{SO}}_3^{2-}$: Central atom is S. Valence electrons = 6. Three oxygen atoms form single bonds. One lone pair on S. Total electron domains = 3 (bond pairs) + 1 (lone pair) = 4. This corresponds to sp3 hybridization and a trigonal pyramidal geometry.
  Both ions have a trigonal pyramidal geometry, so they are isostructural.

Therefore, ${\mathrm{ClO}}_3^{-}$ and ${\mathrm{SO}}_3^{2-}$ are both isoelectronic and isostructural.

Option Analysis:

• A) ${\mathrm{CO}}_3^{2-},{\mathrm{NO}}_3^{-}$:
  Electrons: ${\mathrm{CO}}_3^{2-}$ = 6 + 3*8 + 2 = 32. ${\mathrm{NO}}_3^{-}$ = 7 + 3*8 + 1 = 32. (Isoelectronic)
  Geometry: Both have sp2 hybridization and trigonal planar geometry. (Isostructural)
  Wait, let's recheck the question and options. If A is also correct, there might be an issue with the question or provided answer. Let's re-evaluate.
  Ah, the provided correct answer is D. Let's double check the electron count for D. ClO3- = 17 + 3*8 + 1 = 42. SO3^2- = 16 + 3*8 + 2 = 42. Yes, D is isoelectronic. Both are trigonal pyramidal. So D is correct.
  Let's re-evaluate A. CO3^2- (32 electrons, trigonal planar). NO3- (32 electrons, trigonal planar). So A is also a pair of isoelectronic and isostructural ions. This suggests there might be an error in the question or the provided single correct answer. However, following the provided correct answer D, we will proceed with the analysis of other options to confirm why they are incorrect if D is the *only* correct answer.
• B) ${\mathrm{ClO}}_3^{-},{\mathrm{CO}}_3^{2-}$:
  Electrons: ${\mathrm{ClO}}_3^{-}$ = 42. ${\mathrm{CO}}_3^{2-}$ = 32. (Not isoelectronic)
• C) ${\mathrm{SO}}_3^{2-},{\mathrm{NO}}_3^{-}$:
  Electrons: ${\mathrm{SO}}_3^{2-}$ = 42. ${\mathrm{NO}}_3^{-}$ = 32. (Not isoelectronic)

Given that the provided correct answer is D, and our analysis confirms D is correct, we proceed with D as the answer. It's worth noting that option A also fits the criteria of being both isoelectronic and isostructural.

Correct Answer: (D)