Final answer:
Most nonpolar substances are gases because their molecules are far apart, allowing them to move randomly. Conversely, most polar substances are liquids and solids because their molecules are close together and interact with each other.
Step-by-step explanation:
Most nonpolar substances are gases because the molecules of gases are much farther apart than those of solids and liquids, allowing the particles to move about randomly in space. The forces between gas molecules are considered negligible, except during collisions. On the other hand, most polar substances are liquids and solids because the molecules are closer together, and the behavior of molecules in these substances is highly constrained by their interactions with one another.