GKFix MCQ Question

Which of the following reactions 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)