Which type of molecule cannot mix with water?

Nonpolar molecules cannot mix with water due to their lack of polarity. Water is a polar solvent, meaning it has a partial positive charge on one end (the hydrogen atoms) and a partial negative charge on the other end (the oxygen atom). This polarity allows water molecules to interact with other polar substances, facilitating their dissolution.

In contrast, nonpolar molecules do not have charged regions and cannot form interactions with the polar water molecules. Since they lack the ability to engage in hydrogen bonding or dipole-dipole interactions, they are hydrophobic, meaning they tend to repel water. This is why oil, a classic example of a nonpolar substance, does not mix with water, leading to separate layers when the two are combined.

Polar molecules, like water itself, can mix well due to their attractive forces, and inorganic molecules can also display various solubilities based on their specific nature, while aqueous refers to substances dissolved in water but does not inherently indicate compatibility with water. Thus, nonpolar molecules stand out as those that cannot mix with water.