The correct option is A Graphite is more stable form than diamond
ΔHrxn=ΔHG−ΔHD=−ve, implies that during the transformation of diamond to graphite, energy is released. It is a exothermic reaction. Hence, diamond has more energy than the graphite. Energy is inversly proportional to stability. Thus, Graphile is more stable than diamond.
Here entropy is not changing, Hence enthalpy alone can be used to determine the stability.