. this reaction is
CaCO3 (s) + Heat CaO (s) + CO2 (g)
(A) an endothermic reaction
(B) an exothermic reaction
(C) a reaction that is neither endothermic nor exothermic
(D) a reaction in which a catalyst is used.
Since it is clear from the diagram that energy of products is more then reactant hence energy is absorbed. So it is an endothermic reaction.