Question

how is molecular geometry related to the presence or absence of a molecular dipole moment

Answer 1

Molecules in which the A-X bonds are symmetrical about the central atom (such as the linear, trigonal planar, and tetrahedral geometries) have a zero dipole moment, and are nonpolar. Molecules where the X atoms are not symmetrical (such as the bent and trigonal pyramidal geometries) can have a dipole moment.