Which of the following statements about the molecules of solids and liquids is correct? They both

Analyze the question: We need the one property that is true of the molecules of both solids and liquids.

Concept: Under the kinetic theory of matter:

| Property | Solids | Liquids | Gases | |---|---|---|---| | Intermolecular attraction | Very strong | Moderate | Very weak | | Separation | Very close | Close | Far apart | | Motion | Vibrate about fixed positions | Vibrate, and also move/slide past one another | Random, rapid, free motion |

Checking each option:

• A. Weak attraction: Wrong. Solids have strong forces, and liquids have moderately strong forces. Weak attraction is typical of gases.
• B. Wide separations: Wrong. Molecules in both solids and liquids are closely packed. Wide separations belong to gases.
• C. Random motion: Wrong for solids. Solid molecules are held in fixed positions and cannot move randomly through the substance. Random translational motion is typical of gases (and, to a degree, liquids).
• D. Vibratory motion: Correct. Solid molecules vibrate about fixed positions. Liquid molecules also vibrate (as well as moving past each other), so both exhibit vibratory motion.

Answer: D.

Tip: Remember the pattern for motion: solids vibrate, liquids vibrate and flow, gases move randomly. When a question asks what solids and liquids have in common, look for "close together" or "vibration". Words like "weak" and "wide" or "random" usually point to gases.