Chemical Thermodynamics Part 1

Given :
(i) C(graphite) + O2(g) → CO2(g) ;ΔrH° = x kJ mol−1
(ii) C(graphite) +

1

2

O2 (g) → CO2 (g) ;
ΔrH° = y kJ mol−1
(iii) CO (g) +

1

2

O2 (g) → CO2 (g) ;
ΔrH° = z kJ mol−1
Based on the above thermochemical equations,find out which one of the following algebraicrelationships is correct ?