Final answer:
Carbon dioxide is nonpolar due to its linear geometry and cancellation of dipoles, while water is polar because of its asymmetric bent structure resulting in a charge imbalance.
Step-by-step explanation:
The polarity of a molecule is determined by both its molecular geometry and the electronegativity of its atoms. When comparing carbon dioxide (CO2) and water (H2O), we find that CO2 is a nonpolar molecule because it has a linear structure with two dipoles that cancel each other out. On the other hand, water is a polar molecule because it has an asymmetric bent structure with a molecular dipole, where the oxygen atom has a partial negative charge, and the hydrogen atoms have a partial positive charge.
Solution examples include: Water is polar due to lone pairs of electrons around the central oxygen atom and an asymmetric shape. Methanol is polar owing to its non-symmetric structure with the -OH group inducing polarity. Hydrogen cyanide is polar because of the differing electronegativities between nitrogen and hydrogen. Oxygen is nonpolar, it has a diatomic symmetric structure with equal pull on electrons. Propane is nonpolar because of its symmetric structure with hydrogen atoms evenly distributed and no unshared pairs of electrons.