Top Tips for success (2) IBDP Teacher Blogs, Chemistry | February 10, 2012 Oxidation states / nmubers. Can you list the oxidation state of Cl in the following substances? Cl2O7, HClO4, Cl2O6, ClO3, ClO2, HClO, Cl2, HCl. Click on ‘read more’ below to see the answer… The answers are: