GKFix MCQ Question

Why is the reaction CaO(s) + CO₂(g) → CaCO₃(s) not a standard enthalpy of formation reaction?

• A. The product is not in its standard state
• B. The reaction is exothermic
• C. Calcium carbonate is formed from compounds, not elements
• D. The coefficient of CaCO₃ is greater than 1