What element has the symbol 'At'?

The story behind the answer

‘At’ is the symbol for Astatine, a halogen with atomic number 85. It sits beneath iodine in Group 17 and is extremely rare and radioactive—so much so that only tiny amounts exist naturally. Its name comes from the Greek “astatos,” meaning unstable, reflecting its short-lived isotopes. Scientists study astatine-211 for targeted alpha cancer therapy.

Memory tip: “At is AstaTine—at the end of the halogens.” Don’t confuse it with Arg