Which of the following is NOT a metalloid?

Carbon

The correct answer is option 2. Carbon.

Among the options provided, the element that is NOT a metalloid is carbon.

Carbon is not classified as a metalloid; it is a non-metal. Metalloids are elements that have properties intermediate between those of metals and non-metals, and they are found along the diagonal boundary between metals and non-metals in the periodic table. The other options listed (boron, arsenic, and silicon) are all metalloids.