Question

Both alkaline earth metals and alkali metals are s-block elements. They resemble with each other in many respects but still there are certain dissimilarities in their properties on account of different number of electrons in the valence shell, smaller atomic radii, higher ionisation potential, higher electronegativity, etc.
Like lithium, beryllium also differs from rest of the alkaline earth metals on account of its small atomic size and high electronegativity. Be2+ ion is very small and exerts a high polarising effect on any anion associated with it.
Which is least thermally stable?

1. Li₂CO₃    
2. MgCO₃    
3. BaCO₃    
4. BeCO₃