Which statement about solids is true?

• A. The particles are randomly arranged and can flow past one another.
• B. The particles are arranged in a regular pattern and vibrate about fixed positions.
• C. The particles move freely and occupy all space.
• D. The particles diffuse easily and are loosely packed.

Answer: (B)

Solids have a definite shape and volume because their particles are arranged in an orderly, close-packed structure and cannot move past one another. In crystalline solids, the particles sit in a regular pattern (a lattice) and only vibrate about fixed positions. This limited motion keeps the solid rigid and prevents flow. By contrast, descriptions of random arrangements with flow describe liquids; particles moving freely and occupying all space describe gases; and loose packing with easy diffusion fits many gases or highly energetic states. So the statement that solids have a regular arrangement with vibrations about fixed positions best matches the true behavior of solids.