What defines nonmetals according to their physical characteristics?

Nonmetals are characterized by a distinct set of physical properties that set them apart from metals. The correct answer highlights that nonmetals do not conduct heat or electricity, making them poor conductors, unlike metals which typically do have these conductive properties. Additionally, nonmetals tend to have a dull appearance rather than a shiny one. This lack of luster is another key physical characteristic, as they generally do not exhibit the reflective qualities seen in metals.

In contrast, other choices describe characteristics typical of metals, such as conductivity, malleability, ductility, and a shiny appearance, which do not apply to nonmetals. Thus, the defining traits of nonmetals are accurately captured in this choice, emphasizing their non-conductive nature and lack of shine.