Which of the following is not crystalline?

Correct answer: Plastic. Plastic is amorphous: its particles are not arranged in a regular repeating pattern.

Background: Crystalline solids have a regular internal arrangement and sharp melting points.

• Salt: Salt is a crystalline solid.
• Sugar: Sugar is a crystalline solid.
• Ice: Ice is a crystalline solid.

Did you know? Glass is another well-known amorphous solid.

Memory trick: Crystals: salt, sugar, ice. Amorphous: plastic, glass.