Final answer:
Among the compounds listed, BF3 exhibits a trigonal planar electron geometry. CO2 is linear, CH4 is tetrahedral, and NH3 is trigonal pyramidal in shape. so, option 3 is the correct answer.
Step-by-step explanation:
The student is asking about compounds that have a trigonal planar electron geometry. Among the given options, BF₃ (boron trifluoride) is the compound that has a trigonal planar electron geometry. The fluorine atoms in BF₃ are positioned at the vertices of an equilateral triangle, with angles of 120° between them, and all four atoms (boron and the three fluorines) lie in the same plane. This is consistent with the definition that a molecule with three electron groups adopts the positions of an equilateral triangle, being 120° apart and in a plane, resulting in a trigonal planar shape. CO₂ has a linear electron-pair geometry, CH₄ has a tetrahedral geometry, and NH₃ also has a tetrahedral electron-pair geometry but with a trigonal pyramidal molecular structure.
The compounds with trigonal planar electron geometry are:
CO₂
Beryllium hydride
Boron trifluoride
CO₂ has a linear molecular structure, while Beryllium hydride and Boron trifluoride have trigonal planar molecular structures. In a trigonal planar electron geometry, the three groups are arranged 120° apart in a plane.
Example: In CO₂, the two oxygen atoms are positioned on either side of the carbon atom, forming a linear shape.