Iodine. Fluorine does not form oxyacids.

Which element does not form oxyacid?

(a) In oxy-acids the central elements always exhibits positive oxidation states. Fluorine , being the most electronegative , never shows positive oxidation states, hence F does not form oxy-acids.

Which acid is not oxyacid?

Later, however, Humphry Davy showed that the so-called muriatic acid did not contain oxygen, despite its being a strong acid; instead, it is a solution of hydrogen chloride, HCl. Such acids which do not contain oxygen are nowadays known as hydroacids.