Which of the following materials is classified as brittle?

Brittle materials are characterized by their tendency to break or shatter under stress without significant deformation. Glass is an excellent example of a brittle material because it has a high compressive strength but low tensile strength, making it prone to fracture when subjected to tensile forces. When enough stress is applied, glass does not undergo plastic deformation; instead, it breaks suddenly and catastrophically.

In contrast, aluminum and steel are categorized as ductile materials, meaning they can undergo significant plastic deformation before failure. These metals absorb energy and deform when subjected to stress, which allows for some warning before failure occurs. Rubber, on the other hand, is highly elastic and can stretch considerably without breaking, indicating that it is neither brittle nor capable of shattering under normal conditions. Therefore, glass clearly stands out as the material that exhibits brittle behavior among the choices presented.