The reaction given is called Decomposition reaction.
Explanation:
Here we can see that Magnesium Carbonate (MgCO3) is heated and as a result it has given two compounds which are Magnesium Oxide(MgO) and Carbon Dioxide (CO2).
Decomposition reaction:
A reaction in which a chemical compound breaks into simpler parts in when heat is applied to it.
So,we concluded that the reaction given above is a Decomposition reaction.