The correct order of increasing C-O bond length of CO, CO32-, CO2 is

Bond length ∝1Bond orderBond order : CO32- < CO2 < COBond order in CO = 3 (with the help of molecular orbital theory)Bond order in CO2=No. of bonds in all possible sidesNo. of resonating structure(by resonance)               =42=2Bond order in CO32-=43=1.33 (by resonance) So order to bond length of C-O CO < CO2 < CO32-.