To determine whether a molecule is polar, which information is needed?

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To decide if a molecule is polar, you must know where the dipoles come from and how they add up in three dimensions. That means identifying which bonds are polar (electronegativity differences) and then looking at the molecule’s shape and symmetry to see whether those bond dipoles cancel or reinforce each other. If the geometry is symmetric enough to cancel the dipoles, the molecule is nonpolar even with polar bonds. If the shape is asymmetric so the dipoles do not cancel, the molecule is polar. Bond lengths aren’t the determining factor, and knowing atomic numbers alone doesn’t tell you how the dipoles will combine. For example, a linear, symmetric molecule with polar bonds can be nonpolar due to cancellation, while a bent, asymmetric molecule with polar bonds has a net dipole. So the essential information is the shape, the polar bonds, and the symmetry.