Solids are best described as which of the following?

• A. Solids are highly compressible and have no fixed shape.
• B. Solids have irregular arrangement and can flow.
• C. Solids can move freely past each other.
• D. Solids touch and have a regular arrangement; cannot be compressed; vibrate.

Answer: (D)

In a solid, particles are packed together in a regular pattern and stay in fixed positions relative to one another, held by strong forces. They can only vibrate in place about those positions. This arrangement gives solids a definite shape and a definite volume, because the structure isn’t free to flow or change shape. The particles are so closely packed that compressing a solid is very hard, so solids are effectively incompressible under ordinary pressures. The key idea is that the particles touch and sit in an orderly lattice, with only small vibrations rather than continual movement past each other.