Given: <br> i) $C\left( {{\rm{graphite}}} \right) + {O_2}\left( g \right) \to C{O_2}\left( g \right);\,\,\,\,{\Delta _r}{H^{ \cdot \cdot }} = x\,\,\,kJ\,\,\,mo{l^{ - 1}}$ <br> ii) $C\left( {{\rm{graphite}}} \right) + \frac{1}{2}{O_2}\left( g \right) \to C{O_2}\left( g \right);\,\,\,{\Delta _r}{H^{ \cdot \cdot }} = y\,\,kJ\,\,mo{l^{ - 1}}$ <br> iii) $CO\left( g \right) + \frac{1}{2}{O_2}\left( g \right) \to C{O_2}\left( g \right);\,\,\,\,{\Delta _r}{H^{ \cdot \cdot }} = z\,\,kJ\,\,mo{l^{ - 1}}$ Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?