Final answer:
Silicon (Si) is the metalloid among the given options. Sodium (Na) is an alkali metal, Iron (Fe) is a transition metal, and Chlorine (Cl) is a halogen nonmetal.
Step-by-step explanation:
The element Silicon (Si) is the one among the options provided that is a metalloid. Metalloids have properties that are intermediate between metals and nonmetals. Sodium (Na) is a metal, specifically an alkali metal. Iron (Fe) is a transition metal, and Chlorine (Cl) is a nonmetal, specifically a halogen.
In the periodic table, metalloids are located along the diagonal line from Boron (B) to Astatine (At). Since Silicon (Si) is positioned along this line, oftentimes between the metals on the left and the nonmetals on the right, it is classified as a metalloid.