Which of the following best describes a metalloid?

• A. A metal that conducts electricity well
• B. An element with properties of both metals and nonmetals
• C. A nonmetal that is a gas
• D. A noble gas with low reactivity

Answer: (B)

Metalloids have properties that fall between metals and nonmetals. They often look metallic but behave somewhat like nonmetals, and their ability to conduct electricity is intermediate and can be tuned by factors such as temperature or impurities. This makes them useful as semiconductors in electronics. Because of this mixed behavior, the description that an element has properties of both metals and nonmetals best captures what a metalloid is.

The other descriptions describe a metal that conducts electricity well, a nonmetal that is a gas, and a noble gas that is very unreactive. None of these capture the blend of metallic and nonmetallic characteristics that defines metalloids. For example, a metal that conducts well is not necessarily between metals and nonmetals, a gas nonmetal doesn’t reflect the semi-conductive, intermediate nature, and a noble gas is a distinct group with little in common with metalloids. Common metalloids include silicon and boron, which illustrate this mix of properties.