Which of the following describes nonmetals?

The correct choice effectively identifies the primary characteristics of nonmetals, which are generally recognized for being poor conductors of heat and electricity. This is due to their atomic structure, which does not allow electrons to move freely as they do in metals. Nonmetals tend to have distinct properties compared to metals and are typically found in varied states at room temperature—some are gases, while others are brittle solids.

The other characteristics mentioned in the other choices are indicative of metals. For example, shininess and good thermal and electrical conductivity are hallmark traits of metals, aligning with their ability to allow electrons to flow easily. Conversely, ductility and malleability are traits associated with metals as well, which refer to the ability to deform without breaking. Additionally, many metals possess high melting points, whereas nonmetals often have lower melting points.

Recognizing these properties is crucial for distinguishing between the two broad categories of elements in the periodic table—metals and nonmetals—and helps in understanding their behaviors and applications in chemistry and material science.