Sodium is an earth-metal (group one), sliver and platinum are d-block metals.... Thus silicon is the metalloid and that is true because it looks like a metal being shiny blue-gray but it exhibit non-metal characteristics, except the fact that it can conduct electricity in a heated state.
The group of metalliods in the periodic table include: antimony, arsenic, boron, silicon, germanium, polonium all display semi-metal properties. So the answer would be Silicon.
