Question

which is thermally most stable alkaline earth metal carbonate among mgco3,caco3, srco3, baco3?give reason

Answer 1

MgCO3 is  most stable alkaline earth metal because it is present in first period.Due to this its nuclear charge is less as compare to other.Due to its less nuclear charge its bond length is small thus it is more stable.

Answer 2

From the given options the most thermally stable alkaline earth metal carbonate among Magnesium Carbonate $(\mathrm{MgCO}_{3})$, Calcium Carbonate $(\mathrm{CaCO}_{3})$, Strontium Carbonate $(\mathrm{SrCO}_{3})$, Barium Carbonate $(\mathrm{BaCO}_{3})$ is Magnesium Carbonate $\bold{(\mathrm{MgCO}_{3})}$.  

This is because it has the “smallest atomic number” due to which the size of the molecules or atom is the smallest and most stable. Other options are not as stable as it is because they have a higher atomic number, bigger atomic size and thus the outer electrons are comparatively loosely bound and less “thermally stable”.