Final answer:
Out of the options provided, NH₃ is the only molecule that is polar. NH₃ has a trigonal pyramidal molecular structure due to the lone pair of electrons on nitrogen, which creates an asymmetry in electron distribution, resulting in a polar molecule.
Step-by-step explanation:
To determine which of the following molecules with a trigonal planar electron geometry will be polar, we need to look at the molecular structure and the distribution of electron groups around the central atom. The molecules given are 1) BF₃ 2) CH₄ 3) NH₃ 4) CO₂.
BF₃ has a trigonal planar electron geometry and molecular structure, which means that it is nonpolar because all B-F bonds are of identical polarity and arranged symmetrically, canceling out any dipole moments. CH₄ has a tetrahedral molecular structure, making it nonpolar for similar reasons. NH₃ exhibits a trigonal pyramidal molecular structure, which is polar because the lone pair of electrons on nitrogen creates an asymmetry in the distribution of electron density. Finally, CO₂ has a linear structure, which is nonpolar due to the symmetric arrangement of the double bonds on the central carbon atom.
Therefore, the molecule with a trigonal planar geometry that will be polar is actually NH₃, even though its molecular structure is trigonal pyramidal, which is a common point of confusion.