Standard enthalpies of formation carbon dioxide, water and acetylene are $-390, -286 \mathrm{and} +254 \mathrm{kJ}/\mathrm{mole}$respectively.

Enthalpy of combustion of acetylene is equal to…..kJ/mole

Given,

$$\begin{gathered} \mathrm{C}\left(\mathrm{graphite}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right), ∆\mathrm{H}=-390 \mathrm{kJ}/\mathrm{mole}....\left(1\right) \\ {\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{H}}_2{\mathrm{O}}_{ }\left(\mathrm{l}\right), ∆\mathrm{H}=-286 \mathrm{kJ}/\mathrm{mole}....\left(2\right) \\ 2\mathrm{C}\left(\mathrm{graphite}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)\to {\mathrm{C}}_2{\mathrm{H}}_2\left(\mathrm{g}\right), ∆\mathrm{H}=+254 \mathrm{kJ}/\mathrm{mole}....\left(3\right) \\ \mathrm{Required} \mathrm{equation} \mathrm{is} \\ {\mathrm{C}}_2{\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{5}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ 2\times \mathrm{Eq}\left(1\right)+\mathrm{Eq}\left(2\right)-\mathrm{Eq}\left(3\right)=\mathrm{Required} \mathrm{equation} \\ 2\left(-390\right)+\left(-286\right)-\left(+254\right)=\mathrm{Required} \mathrm{equation} \\ -780-286-254=\mathrm{Required} \mathrm{equation} \\ {∆}_{\mathrm{c}}^0\left({\mathrm{C}}_2{\mathrm{H}}_2\right)=-1320 \mathrm{kJ}/\mathrm{mole} \end{gathered}$$