While performing an experiment involving a reaction between two chemicals, the scientist observes that the reaction container has become warm. the observation is an example of:

Explanation:

In an exothermic reaction, heat is released into the surroundings. In this type of reaction, energy of products is less than the energy of reactants.

In an endothermic reaction, heat is absorbed by the reactant molecules. In this type of reaction, energy of products is more than the energy of reactants.

Therefore, we can conclude that while performing an experiment involving a reaction between two chemicals, the scientist observes that the reaction container has become warm. The observation is an example of exothermic reaction.