Hydrogenation of unsaturated hydrocarbons is an exothermic reaction. Due to hyperconjugation and resonance the stability of unsaturated hydrocarbons increases and the increase in stability is more due to resonance. Compound with same number of `pi-`bonds and more stability has lower heat of hydrogenation.
Heat of formation is defined as the energy evolved when a molecule is formed from its atoms. For isomers the more stable compounds has higher heat of formation.
The order of heat of formation of the following molecules is :
A. `IgtIIgtIIIgtIV`
B. `IIgtIIIgtIVgtI`
C. `IVgtIIgtIIIgtI`
D. `IVgtIIIgtIIgtI`
