Which term describes liquids that do not mix to form a single phase?

• A. Solubility
• B. Miscible
• C. Hydration
• D. Immiscible

Answer: (D)

Liquids that do not mix to form a single phase are immiscible. When two liquids are immiscible, they separate into distinct layers because their molecules prefer interactions with like molecules over mixing with the other liquid. A classic example is oil and water: water is polar and forms strong hydrogen bonds, while oil is nonpolar, so the attraction between water and oil is weak. This makes mixing energetically unfavorable, so they stay as two separate phases instead of one uniform liquid.

This contrasts with miscible, where liquids mix completely to form a single homogeneous phase, like ethanol and water. Hydration and solubility describe other ideas—hydration involves water molecules surrounding particles in solution, and solubility is about how much of a substance can dissolve in a solvent—neither of which specifically define two liquids that fail to mix into one phase.