The correct order of increasing thermal stability of K₂CO₃, MgCO₃, CaCO₃ and BeCO₃ is

In which of the following the hydration energy is higher than the lattice energy?

The correct order of the mobility of the alkali metal ions in aqueous solution is

A solid compound X on heating gives CO₂ gas and a residue. The residue mixed with water forms Y. On passing an excess of CO₂ through Y in water, a clear solution Z is obtained. On boiling Z, compound X is reformed. The compound X is