The molecular geometry of ammonia NH3 is trigonal pyramidal. In this structure, the nitrogen atom is at the center, and the three hydrogen atoms surround it, forming a pyramid-like shape. The nitrogen atom also has a lone pair of electrons, which contributes to the overall shape of the molecule.The bond angles in ammonia are approximately 107.5 degrees. This is slightly smaller than the ideal tetrahedral angle of 109.5 degrees, due to the repulsion between the lone pair of electrons on the nitrogen atom and the bonding pairs of electrons between the nitrogen and hydrogen atoms.Ammonia is a polar molecule because it has a net dipole moment. This is due to the difference in electronegativity between the nitrogen and hydrogen atoms, which causes the bonding electrons to be more attracted to the nitrogen atom. This creates a partial negative charge on the nitrogen atom and partial positive charges on the hydrogen atoms. The trigonal pyramidal geometry of ammonia ensures that these individual bond dipoles do not cancel each other out, resulting in a net molecular dipole moment.In summary, the trigonal pyramidal molecular geometry and bond angles of ammonia contribute to its polarity and dipole moment by ensuring that the individual bond dipoles do not cancel each other out, resulting in a net molecular dipole moment.