Now, in the final step, once we actually form this polypeptide chain, what we have to do is a, we have to break this bond here and detach our polypeptide from this solid surface and b, we also want to remove this T bog group. Now, the tea bog group can be simply removed by mixing it with this molecule here. But how do we break this bond here? So the question is, how do we break this bond without breaking any of the peptide bonds in that polypeptide chain? Well, we have to mix it with hydrofluoric acid. If we mix it with HF in the presence of this molecule here, that essentially removes this teapot group and any other blocking group found on any of the side chains.