Answer:

i) Carbonate thermal stability rises with cationic size. The more stable an alkaline earth metal’s oxide, the less stable its carbonate. As BeO is stable, BeCO3 is not.

(ii) Alkali metals generate metal oxides with oxygen. Except for BeO, which is amphoteric. They also react with water to generate hydroxides. BeO and MgO have the highest lattice energy and are insoluble in water.