Which term describes 'water fearing' molecules that do not mix with water?

• A. Biosphere
• B. Hydrophobic
• C. Ecosystem
• D. Hydrophilic

Answer: (B)

Water is a polar molecule, so substances that are nonpolar don’t form favorable interactions with it. Molecules that are nonpolar—lacking charged regions—are described as hydrophobic, meaning they tend to avoid water and don’t mix with it. In water, these hydrophobic compounds cluster together to minimize contact with the surrounding water, which is why oils and fats separate from water and why cell membranes have hydrophobic interiors that keep water-soluble substances out.

The other terms aren’t about how a substance interacts with water: biosphere and ecosystem refer to levels of biological organization, not molecular behavior, and hydrophilic describes water-loving, polar or charged substances that readily dissolve in water.