Solution of the 228 on the chemistry of Shimanovich IL 2001-2004

228. Based on the oxidation state of chromium, iodine and sulfur compounds K2Cr2O7, KI and H2SO3, define; Which of these is only an oxidant and a reductant only may exhibit both oxidising and reducing properties. Why is that? On the basis of the electronic set up the coefficients of the equations in the equation reaction occurring under the scheme: NaCrO2 + PbO2 + NaOH -> Na2CrO4 + Na2PbO2 + H2O