Which material is characterized as hard, brittle, and composed of metallic and nonmetallic elements?

The correct choice is characterized by its unique composition and properties. Specifically, ceramics are materials that consist of both metallic and nonmetallic elements. This combination allows ceramics to exhibit significant hardness, making them resistant to wear and deformation. Additionally, the atomic structure of ceramics often leads to brittleness. While they can withstand high temperatures and exhibit low thermal and electrical conductivity, they are not ductile, which contributes to their brittle nature.

Plastics, on the other hand, are generally more flexible and not hard or brittle in the same way ceramics are. Composites are materials made from two or more constituent materials that retain their distinct properties, and they usually combine the advantages of both components rather than adhering solely to the characteristics mentioned. Glass, while hard and brittle, is predominantly nonmetallic and does not contain the metallic elements that define ceramics. Thus, ceramics stand out as the material that aligns precisely with the described traits.