Final answer:
Isopropyl alcohol is the best compound to help water and gasoline mix because it has both a polar and nonpolar part. It can bond with water through hydrogen bonding and interact with gasoline through dispersion forces.
Step-by-step explanation:
When considering the mixing of two substances with different polarity, such as water and gasoline, the intermolecular interactions are of great importance. Water molecules display strong hydrogen bonding among themselves which is why polar or ionic compounds can dissolve well in water but nonpolar compounds like gasoline do not mix well. A compound that may help these two substances mix into a single liquid phase should be able to interact with both polar and nonpolar molecules.
Option a, isopropyl alcohol, is the best choice among the given options. It contains both a polar hydroxyl group that can form hydrogen bonds with water and a nonpolar hydrocarbon chain that can interact with nonpolar substances like gasoline. Therefore, isopropyl alcohol acts as a bridge between the water and gasoline molecules, aiding in the formation of a homogeneous solution.
In contrast, option b, sodium chloride, is very polar due to being composed of ions and would not interact effectively with nonpolar gasoline. Option c, methane, is nonpolar and would not help mix the two substances. These selections are informed by the concept of 'like dissolves like' which posits that substances with similar types of intermolecular forces are more likely to mix well.