1. CO32− and SO32− : - CO32− : Carbonate ion has 4(C)+3×6(O)+2 (charge) =24 electrons. - SO32− : Sulfite ion has 6(S)+3×6(O)+2 (charge) =26 electrons. - These ions are not isoelectronic. 2. ClO3−and CO32− : - ClO3−: Chlorate ion has 7(Cl)+3×6(O)+1 (charge) =26 electrons. - CO32− : Carbonate ion has 24 electrons. - These ions are not isoelectronic. 3. SO32− and NO3−: - SO32− : Sulfite ion has 26 electrons. - NO3−: Nitrate ion has 5(N)+3×6(O)+1 (charge) =24 electrons. - These ions are not isoelectronic. 4. ClO3−and SO32− : - ClO3−: Chlorate ion has 26 electrons. - SO32− : Sulfite ion has 26 electrons. - These ions are isoelectronic. - Both ions have a trigonal pyramidal structure. - These ions are isostructural. Therefore, the correct pair is ClO3−and SO32−.