Which of the following pairs of species is isoelectronic but NOT isostructural?

Step-by-step solution

Two species are isoelectronic if they have the same total number of electrons, and isostructural if they have the same molecular geometry. For CO ₃²⁻ ( 6 + 24 + 2 = 32 electrons) and NO ₃⁻ ( 7 + 24 + 1 = 32 electrons): They are isoelectronic. Both have sp ^2 hybridized central atoms with no lone pairs, so both are trigonal planar. They are isostructural. For NH ₃ ( 7 + 3 = 10 electrons) and H ₃ O ⁺ ( 8 + 3 - 1 = 10 electrons): They are isoelectronic. Both have sp ^3 hybridized central atoms with one lone pair, so b