GKFix MCQ Question

Which of the following is NOT a standard enthalpy of formation?

• A. H₂(g) + ½O₂(g) → H₂O(l)
• B. C(graphite, s) + 2H₂(g) → CH₄(g)
• C. CaO(s) + CO₂(g) → CaCO₃(s)
• D. ½H₂(g) + ½Br₂(l) → HBr(g)