Which term describes a molecule that is repelled by water?

• A. Hydrophobic
• B. Hydrophilic
• C. Amphipathic
• D. Lipophilic

Answer: (A)

Molecules that avoid water are hydrophobic. This happens because they’re nonpolar and can’t form favorable interactions with polar water molecules. Water prefers to hydrogen-bond with other polar or charged groups, so nonpolar regions are pushed away, causing hydrophobic substances to cluster together and separate from water. That’s why fats and many oils don’t mix with water.

In contrast, hydrophilic substances are polar or charged and dissolve readily in water. Amphipathic molecules have both hydrophobic and hydrophilic parts, so they can interact with both lipids and water, often lining up at interfaces like cell membranes. Lipophilic describes lipid-loving or fat-soluble compounds, which often behave similarly to hydrophobic substances but with emphasis on affinity for lipids rather than water.