Which of the following statement is correct for the reaction?CaO(s)+CO2(g)⟶CaCO3(s)                                      ΔrH∘=−178.3kJmol−1

A standard molar enthalpy of formation, ΔfH∘ is just a special case of ΔrH∘, where one mole of a compound is formed from its constituent elements.CaO(s)+CO2(g)⟶CaCO3(s)                                     ΔrH∘=−178.3kJmol−1It is not an enthalpy of formation of CaCO3, since CaCO3 has been formed from other compounds and not from its constituent elements.