Explanation:
Thermal stability of carbonates of II A group increases down the group due to increase in size of metal cation.
\({\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\rm{BeC}}{{\rm{O}}_{\rm{3}}}{\rm{ < }}\,{\rm{MgC}}{{\rm{O}}_{\rm{3}}}{\rm{ < }}\,{\rm{SrC}}{{\rm{O}}_{\rm{3}}}{\rm{ < }}\,{\rm{BaC}}{{\rm{O}}_{\rm{3}}}\)
\(\,\,\,523{\rm{K}}\,\,\,\,\,\,\,\,\,813{\rm{K}}\,\,\,\,\,\,\,\,\,\,1562{\rm{K}}\,\,\,\,\,\,1633{\rm{K}}\)