Chemistry - Thermodynamics - I Question with Solution | TestHub

If $C$ (diamond $)\to C$ (graphite $)+\mathrm{X}\mathrm{kJ}{\mathrm{mol}}^{-1}$
$\mathrm{C}($ diamond $)+{\mathrm{O}}_2(\mathrm{g})\to {\mathrm{CO}}_2(\mathrm{g})+\mathrm{Y}\mathrm{kJ}{\mathrm{mol}}^{-1}$
C (graphite) $+{\mathrm{O}}_2(\mathrm{g})\to {\mathrm{CO}}_2(\mathrm{g})+\mathrm{Z}\mathrm{kJ}{\mathrm{mol}}^{-1}$
at constant temperature. Then