Which property should engineers look for in a material that can be stretched and reduced in cross-section without breaking?

Ductility refers to a material's ability to undergo significant plastic deformation before rupture or fracture. When a ductile material is stretched, it can elongate and change its shape while maintaining its integrity, which is crucial in engineering applications. This property is essential in processes such as drawing, rolling, or stretching metals as it allows for various shapes and components to be formed without compromising the material's performance.

Plasticity, while related to ductility, primarily describes the ability of a material to undergo permanent deformation when a stress is applied. Although both ductility and plasticity are important, ductility specifically emphasizes the ability to stretch without breaking, making it the more relevant characteristic for this question.

Brittleness describes a material that tends to fracture with little or no plastic deformation, which is the opposite of what is desired when stretching a material. Toughness is a measure of a material's ability to absorb energy and plastically deform without fracturing; however, it does not specifically focus on the ability to stretch and reduce in cross-section.

Therefore, ductility is the key property engineers look for in a material that can be stretched and reduced in cross-section without breaking.