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 _____.

HCOOH + H2SO4 → CO + H2O.. (i)
(COOH)2 + H2SO4 → CO + CO2 + H2O.. (ii)
Conc. H2SO4 is a strong dehydrating agent.
Moles of HCOOH = 2.3/46 = 0.05 mole
Moles of (COOH)2 = 4.5/90 = 0.05 mole
From reaction (i),
Number of CO formed = 0.05 mole
From reaction (ii),
Number of CO formed = 0.05 mole
Number of CO2 formed = 0.05 mole
Hence, total CO formed = 0.05 + 0.05 = 0.1 mole
total of CO2 formed = 0.05 mole
KOH pellets absorbs all CO2, H2O is absorbed by H2SO4 thus CO is remaining product.
Thus, the weight of the remaining product = 0.1 × 28 = 2.8 g.
Hence, the correct option is B