On the basis of thermochemical equations (i), (ii) and (iii), find out which of the algebraic relationships given in options is correct. (i) \(\mathrm{C}(\mathrm{graphite}) + \mathrm{O}_2(\mathrm{g})\rightarrow \mathrm{CO}_2(\mathrm{g}); \Delta_{\mathrm{r}}H = \mathrm{x}\mathrm{kJ}\mathrm{mol}^{-1}\) (ii) \(\mathrm{C}(\mathrm{graphite}) + \frac{1}{2}\mathrm{O}_2(\mathrm{g})\rightarrow \mathrm{CO}(\mathrm{g}); \Delta_{\mathrm{r}}H = \mathrm{y}\mathrm{kJ}\mathrm{mol}^{-1}\) (iii) \(\mathrm{CO}(\mathrm{g}) + \frac{1}{2}\mathrm{O}_2(\mathrm{g})\rightarrow \mathrm{CO}_2(\mathrm{g}); \Delta_{\mathrm{r}}H = \mathrm{z}\mathrm{kJ}\mathrm{mol}^{-1}\)