Arrange the following in the decreasing order of leaving group ability:

(I) ^-OAc (II) ^-OMe (III) ^-OSO₂Me (IV) CF₃SO₂O^-

IV > III > I > II

Weaker the base better is the leaving group. Now acidity decreases in the order : CF₃SO₂OH > MeSO₂OH > AcOH > MeOH, therefore basicity of their conjugated bases increases in the reverse direction, i.e., CF₃SO₂O^- < MeSO₂O^- < AcO^- < MeO^-