In the reaction the stoichimetric coefficients of Cr2O72−, NO2−  and H+ respectively are : Cr2O72−+NO2−+H+→Cr+3+NO3−+H2O

The balanced stoichiometric  chemical equation  is Cr2O72−+3NO2−+8H+→2Cr+3+3NO3−+4H2O Hence the stoichiometric coefficients ofCrO72−,NO2−  and H+  would be 1,3,8.