Carbonates (MCO3): Stability increases down the group. BeCO3 < MgCO3 < CaCO3 < SrCO3 < BaCO3. Explanation: Small, highly charged $M^{2+}$ cation polarises the large $CO3^{2-}$ anion (distorts electron cloud), weakening a C-O bond and facilitating decomposition to MO + CO2. Larger cations ($Ba^{2+}$) polarise less → more stable carbonate. BeCO3 is so unstable it only exists in CO2 atmosphere. Hydroxides: Same trend — Be(OH)2 decomposes easily, Ba(OH)2 is very stable. Nitrates: All decompose on heating: 2M(NO3)2 → 2MO + 4NO2 + O2. Stability increases down the group. Sulphates: Thermal stability also increases down the group (BeSO4 decomposes at lowest temperature).