Solve this following

Given :

(i) $\mathrm{C}$ (graphite) $+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g})$;

$\Delta \mathrm{rH}^{\circ}=\mathrm{x} \mathrm{kJ} \mathrm{mol}^{-1}$

(ii) $\mathrm{C}$ (graphite) $+\frac{1}{2} \mathrm{O}_{2}$ (g) $\rightarrow \mathrm{CO}_{2}(\mathrm{~g})$;

$\Delta \mathrm{rH}^{\circ}=\mathrm{y} \mathrm{kJ} \mathrm{mol}{ }^{-1}$

(iii) $\mathrm{CO}(\mathrm{g})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g})$;

$\Delta \mathrm{rH}^{\circ}=\mathrm{z} \mathrm{kJ} \mathrm{mol}-1$

Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?