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

1. Formic acid ($\text{HCOOH}$): Moles $=\frac{2.3}{46}=0.05\text{mol}$.Dehydration: $\text{HCOOH}\stackrel{{\text{H}}_2{\text{SO}}_4}{\to }\text{CO}+{\text{H}}_2\text{O}$.Gas evolved: $0.05\text{mol}$ of $\text{CO}$.2. Oxalic acid ($(\text{COOH}{)}_2$): Moles $=\frac{4.5}{90}=0.05\text{mol}$.Dehydration: $(\text{COOH}{)}_2\stackrel{{\text{H}}_2{\text{SO}}_4}{\to }\text{CO}+{\text{CO}}_2+{\text{H}}_2\text{O}$.Gases evolved: $0.05\text{mol}$ of $\text{CO}$ and $0.05\text{mol}$ of ${\text{CO}}_2$.3. Total gases: $\text{CO}=0.05+0.05=0.1\text{mol}$; ${\text{CO}}_2=0.05\text{mol}$.4. Passing through $\text{KOH}$: ${\text{CO}}_2$ is absorbed by $\text{KOH}$. $\text{CO}$ is not.5. Remaining product is $\text{CO}$.Weight $=\text{moles}\times \text{molar mass}=0.1\times 28=2.8\text{g}$.