Please explain these question

Thermal stabilty of 1a group increase down the group therefore k2co3 is the answer

On thermal decomposition: MgCO3​→MgO+CO2​ Li2​CO3​→Li2​O+CO2​ ZnCO3​→ZnO+CO2​ All of the above compounds gives oxides. Hence option D is correct.ie K2CO3

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