A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$. The evolved gaseous  mixture is passed through KOH pellets. Weight (in g) of the remaining product at STP will be

$\underset{\text{ Formic acid }}{\mathrm{HCOOH}}\stackrel{\text{ Conc. }{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}\mathrm{CO}+{\mathrm{H}}_2\mathrm{O}$
$\underset{\text{ oxalic acid }}{(\mathrm{COOH}}{)}_2\stackrel{\text{ Conc. }{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}\mathrm{CO}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$
CO remains at STP.
CO from 4.5 g of oxalic acid
$=\frac{4.5}{90}\times 28=1.4\mathrm{g}$
CO from 2.3 g of formic acid
$=\frac{2.3}{46}\times 28=1.4\mathrm{g}$
Weight of CO = 1.4 + 1.4 = 2.8 g