Identify the chemical reaction which is not an exothermic reaction from the given options:

The correct answer is: Thermal Decomposition

The correct option is d) Thermal Decomposition.
Thermal decomposition is a chemical reaction in which heat is the reactant. These reactions are endothermic because heat is the reactant. In other words, the reaction requires heat energy to break the chemical bonds within the molecule. A common example is calcination.