The heats of combustion of carbon, hydrogen and acetylene are –394K.J, – 286K.J and –1301 K.J respectively. Calculate heat of formation of $C_2{H}_2$.

 The reactions are given below:

$$\begin{gathered} C+O_2\to C{O}_2;\Delta \text{H=-394 KJ}.......\text{(i)} \\ {\text{H}}_2+\frac{1}{2}{O}_2\to H_{2}O;\Delta \text{H=-286 KJ}.......\text{(ii)} \\ {\text{C}}_2{H}_2+\frac{5}{2}{O}_2\to 2C{O}_2+H_{2}O;\Delta \text{H=-1301 KJ}.......\text{(iii)} \end{gathered}$$

The required reaction is:

$2C+H_2\to C_2{H}_2$ 

The reaction and the enthalpy can be calculated as:

$2\times \left(i\right)+\left(ii\right)-\left(iii\right)$ 

So, the enthalpy will be:

$$\begin{gathered} \Delta \text{H = 2 }\times \text{ -394 + (-286) - (-1301)} \\ \Delta \text{H = 227 KJ} \end{gathered}$$

Therefore, the correct option is D.