Which of the following materials is considered brittle?

The correct answer is cast iron, which is classified as a brittle material due to its microstructure. Brittle materials are characterized by their tendency to fracture without significant deformation or plasticity when subjected to stress. Cast iron contains a high carbon content, which leads to the formation of graphite flakes in its structure. This microstructural arrangement makes it susceptible to cracking under tensile stress, while it can still withstand compressive loads to some extent.

In contrast to cast iron, softened brass is more malleable and ductile, allowing it to deform rather than break when force is applied. Low carbon steel, which has a lower carbon content, is known for its toughness and ability to undergo significant deformation before fracture, making it much more resilient under stress. Copper, similarly, is recognized for its ductility and ability to be drawn into wires or pounded into sheets without breaking. These properties differentiate cast iron as the clear representative of brittleness among the given options.