The thermal stability of BaCO3, CaCO3, SrCO3 and MgCO3 decreases in the order : — s Block Elements Chemistry Question

💡 Solution & Explanation

Step 1: The thermal decomposition of Group 2 carbonates yields a metal oxide and carbon dioxide (MCO3 -> MO + CO2). The ease of decomposition depends on the polarizing power of the metal cation. Step 2: Smaller cations with high charge density (like Mg^2+) strongly polarize the carbonate anion, facilitating its decomposition at lower temperatures. Down the group, cationic size increases (Mg^2+ < Ca^2+ < Sr^2+ < Ba^2+), decreasing polarizing power and increasing thermal stability. Step 3: Therefore, stability decreases in the order BaCO3 > SrCO3 > CaCO3 > MgCO3, matching option (d).