The only metalloid in group 17 is astatine (At).

Quick Scoop

Group 17 of the periodic table is the halogen group, which includes fluorine, chlorine, bromine, iodine, astatine, and tennessine. All of these are generally classified as nonmetals, but astatine is often described as having metalloid‑like character because its properties are intermediate between typical metals and nonmetals.

Astatine is extremely rare and highly radioactive, so its physical and chemical behavior is mostly inferred from theory and very limited experiments. Those studies suggest astatine is less volatile, more polarizable, and more metal‑like than iodine, which is why many sources treat it as the only metalloid‑type element in group 17.

So, filling in the sentence “the only metalloid in group 17 is …” — the answer is astatine (At).

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