What is a crystalline solid?

• A. A liquid with no long-range order.
• B. A gas with molecules.
• C. Atoms, ions, or molecules that make up a solid in a regular, well-defined arrangement.
• D. A powder with random grains.

Answer: (C)

A crystalline solid is built from atoms, ions, or molecules arranged in a regular, repeating pattern that extends in all directions to form a crystal lattice. This long-range order fixes the positions of its constituents, giving the material a definite shape, flat faces, and often a sharp melting point. It also leads to characteristic diffraction patterns when X-rays interact with the structure.

In contrast, a liquid has no long-range order and can flow to assume the container’s shape, and a gas has no fixed positions at all. A powder with random grains suggests a disordered assembly rather than a single, well-ordered lattice, so it doesn’t embody the same extended periodic arrangement. Hence, the description of a regular, well-defined arrangement of building blocks best defines a crystalline solid.