If B–Cl bond has a dipole moment, explain why $BC{I}_{3}$ molecule has zero dipole moment.

As a result of the difference in the electronegativities of B and Cl, the B–Cl bond is polar in nature. However, the $BC{I}_{3}$ molecule is non-polar. This is because $BC{I}_{3}$ is trigonal planar in shape. It is a symmetrical molecule. Hence, the respective dipole-moments of the B–Cl bond cancel each other, thereby causing a zero-dipole moment.