Resonance structure and average bond order SO₄ ^2- CH₃COO^- HCO₃^- and NO₃^-
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In sulphate ion there are total six bonds around the sulphur atom with four oxygen atoms in every structure so the average bond order is 6 / 4 that is 1.5
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In acetate ion, carbon central atom has  three bonds with two oxygen atoms in every resonating structure.
So the average bond order is 300/2 batteries 1.5
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In hydrogen carbonate ion carbon is a central atom and it has 4 bonds with three oxygen atoms in every resonating structure so the bond order is 4 /3 = 1.3333

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In nitrate ion ,central element is nitrogen and is bonded to three oxygens using four bonds in every resonating structure.
So the bond order is 4 /3=1.3333