Classification Of Elements And Periodicity In Properties

The formula of a noble gas species that is isostructural with BrO₃⁻ (bromate ion) is XeO₃.

Isostructural species have the same molecular or polyatomic ion structure. In this case, both BrO₃⁻ and XeO₃ have a trigonal pyramidal structure, where the central atom (Br or Xe) is surrounded by three oxygen atoms.

Therefore, the correct answer is XeO₃.