When the carbon-oxygen bonds in ${\mathrm{H}}_3\mathrm{COH}, {\mathrm{H}}_2\mathrm{CO}$ and ${\mathrm{HCO}}_2^{-}$ are arranged in order of increasing length, what is the correct order?

${\mathrm{H}}_2\mathrm{CO}$ has single bond character while ${\mathrm{HCO}}_2^{-}$ has double bond character and ${\mathrm{H}}_3\mathrm{COH}$ has partial double bond character. Hence B.L. order: II< Ill< I.