Question

The carbonate which will not decompose on heating is

Answer 1

Most carbonates tend to decompose on heating to give the metal oxide.
For example, a typical group 2 carbonate like calcium carbonate decomposes like this :in group 1 lithium carbonate behaves in the same way - producing lithium oxide and carbon dioxide

Answer 2

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carbonates on heating decompose into their respective oxides and a gas is evolved but there are some carbonates that do not decompose

example :- sodium carbonate (na2co3) where no gas is evolved and no oxide is formed