On heating, lead (II) nitrate gives a brown gas (A). The gas (A) on cooling changes to a colourless solid/liquid (B). (B) on heating with NO changes to a blue solid (C). The oxidation number of nitrogen in solid (C) is :

PbNO32(s)⟶ΔPbO(s)+NO2(g)+O2(g)                             Brown gas                                      (A)2NO2(g)⟶ Cooling N2O4(A)                   colorless (B) N2O4+NO⟶N2O3colourless (B)     Blue solid (C)Oxidation number of nitrogen in solid (C) is +3