Which expression correctly gives the standard enthalpy change ΔHrxn∘ for the reaction 2NO(g)+O2(g)→2NO2(g) in terms of the standard enthalpies of formation ΔHf∘ of the species involved?
a) 2ΔHf∘(NO)+ΔHf∘(O2)−2ΔHf∘(NO2)
b) 2ΔHf∘(NO2)−2ΔHf∘(NO)
c) 2ΔHf∘(NO2)−[2ΔHf∘(NO)+ΔHf∘(O2)]
d) ΔHf∘(NO2)−[ΔHf∘(NO)+ΔHf∘(O2)]