Which of these elements would most likely be a metalloid?

Silicon is classified as a metalloid because it exhibits properties that are characteristic of both metals and nonmetals. In the periodic table, metalloids are typically found between metals and nonmetals, and they often have intermediate properties. Silicon, for instance, is a good conductor of electricity at certain temperatures, making it useful in electronic devices, while also being brittle like nonmetals. This unique combination of properties exemplifies what defines metalloids.

In contrast, sodium is a highly reactive metal, chlorine is a reactive nonmetal, and copper is a well-known metal with excellent conductivity. These elements do not share the intermediate characteristics that typify metalloids like silicon.