GKFix MCQ Question

What is the correct expression for Kp for the reaction CaCO₃(s) ⇌ CaO(s) + CO₂(g)?

• A. Kp = P_CO₂
• B. Kp = 1 / P_CO₂
• C. Kp = P_CaO / P_CaCO₃
• D. Kp = P_CaCO₃ / P_CaO