Given three reaction below, $N_2(g) + 3H_2(g) \leftrightharpoons 2NH_3(g); \Delta H_1$, $H_1(g) + Cl_2(g) \leftrightharpoons 2HCl(g) ; \Delta H_2$, $NH_3 (g) + 3Cl_2 \leftrightharpoons NCl_3(g) + 3HCl(g); -\Delta H_3$. In the terms of $\Delta H_1, \Delta H_2$ and $\Delta H_3$, heat of formation of $NCl_3(g)$ is

Question

(a) $\Delta H_f = -\Delta H_3 + \frac{\Delta H_1}{2} - \frac{3}{2} \Delta H_2$
(b) $\Delta H_f = \Delta H_3 + \frac{\Delta H_1}{1} - \frac{3}{2} \Delta H_2$
(c) $\Delta H_f = \Delta H_3 -\frac{\Delta H_1}{2} - \frac{3}{2} \Delta H_2$
(d) None of the above