In III, bond order of C—N bond is = 2 In II, bond order of C—N bond is = 1 In I and IV, delocalization of nitrogen lone pair take place, so bond order is between 1 and 2. But in IV, delocalization of nitrogen lone pair is more than delocalization of nitrogen lone pair in I, as delocalization in IV, brings negative charge on oxygen, while in I, it brings negative charge on carbon. Hence C-N bond in IV acquire greater partial double bond character. So bond order of IV > Bond order of I Bond Order, III > IV > I > II Greater the bond order lesser the bond length Bond length, III < IV < I < II