Which of the following molecules does NOT have trigonal planar electron-pair geometry?

• A. SO_3
• B. CO_3^{2-}
• C. NH_3
• D. BF_3

Answer: (C)

Verified step by step guidance

1. Recall that trigonal planar electron-pair geometry occurs when a central atom has three regions of electron density (bonding or lone pairs) arranged around it in a plane, with approximately 120° bond angles.
2. Analyze each molecule or ion to determine the number of electron regions around the central atom:
3. For SO_3, the sulfur atom is bonded to three oxygen atoms with no lone pairs, so it has three regions of electron density, which corresponds to trigonal planar geometry.
4. For CO_3^{2-}, the central carbon atom is bonded to three oxygen atoms with no lone pairs, also giving three regions of electron density and trigonal planar geometry.
5. For NH_3, the nitrogen atom has three bonding pairs and one lone pair, totaling four regions of electron density, which corresponds to a tetrahedral electron-pair geometry, not trigonal planar.