(a) Thermal stability of group 2 carbonates : The thermal stability of carbonates of alkaline earth metals increases down the group as the cation's polarising power decreases. The order BeCO3<MgCO3<CaCO3<SrCO3 is correct. (b) Solubility of group 2 sulphates: The solubility of sulphates of alkaline earth metals decreases down the group. The order BeSO4>MgSO4>CaSO4>SrSO4 is correct. (c) Thermal stability of group 1 carbonates : The thermal stability of alkali metal carbonates increases down the group as the cation's polarising power decreases. The correct order is Li2CO3<Na2CO3<K2CO3<Rb2CO3 The given order, Li2CO3>Na2CO3>K2CO3>Rb2CO3, is the reverse and therefore incorrect. (d) Solubility of group 2 carbonates: The solubility of alkaline earth metal carbonates decreases down the group. The order BeCO3>MgCO3>CaCO3>SrCO3 is correct. Thus, the incorrect order is (c)..