GKFix MCQ Question

Which of the following reactions is a standard enthalpy of formation?

• A. CaO(s) + CO₂(g) → CaCO₃(s)
• B. H₂(g) + Br₂(l) → 2HBr(g)
• C. C(graphite, s) + 2H₂(g) → CH₄(g)
• D. All of the above