A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc. H2SO4. The evolved gaseous  mixture is passed through KOH pellets. Weight (in g) of the remaining product at STP will be

H2O absorbed by H2SO4. Gaseous mixture (containing CO and CO4) when passed through KOH pellets, CO2 gets absorbed. Moles of CO left (unabsorbed) =120+120=110 Mass of CO= moles × molar mass                              =110×28=2.8 g