Here's why:

* Physical Properties: Iodine is a solid at room temperature, but it readily sublimates (turns directly from solid to gas) when heated. It has a dark purple-black color and is lustrous, but it is brittle and not a good conductor of heat or electricity.

* Chemical Properties: Iodine is a highly reactive element, forming salts (iodides) with metals and reacting with other nonmetals. It is known for its antimicrobial properties.

While some metalloids, like arsenic and selenium, can also be brittle, iodine's chemical properties clearly place it in the nonmetal category.