Complex sentence: Perbromic acid is unstable and cannot be formed by displacement of chlorine from perchloric acid, as periodic acid is prepared; it can only be made by protonation of the perbromate ion.
Split into simpler sentences: Perbromic acid is unstable and cannot be formed by displacement of chlorine from perchlorate, as periodates are prepared. It can only be made by protonation of the perbromate ion.