When $2g$ of oxalic acid $\left(H_2{C}_2{O}_4\right)$ is burned in a bomb calorimeter whose heat capacity is $8.75KJ{K}^{-1},$ the temperature increased by $0.312k.$ The enthalpy of combustion of oxalic acid at $300k$ is

$H_2{C}_2{O}_4\left(l\right)+\frac{1}{2}{O}_2\left(g\right)\to H_{2}O\left(l\right)+2C{O}_2\left(g\right)$

$\Delta n=2-\frac{1}{2}=\frac{3}{2}$

In Bomb Calorimeter $\text{'}V\text{'}$ is constant $\therefore \Delta E=\frac{-Z\times \theta \times M}{m}=\frac{-8.75\times 0.312\times 90}{2}=-122.85KJmo{l}^{-1}$

$\therefore$Enthalpy of combustion $\begin{array}{l}\left(\Delta H\right)=\Delta E-\Delta n.RT=-122.85-\frac{3}{2}\times \frac{8.3}{1000}\times 300=-126.6KJ/mol\end{array}$