Answer: Option (A) is the correct answer.
Explanation:
A chemical reaction in which there will be release of heat energy by the reactant molecules is known as an exothermic reaction.
For example, [tex]A + B \rightarrow CD + Heat[/tex]
Also, according to law of conservation of mass energy gained by the reactants will be equal to the amount of energy lost to the surroundings. This is because energy can neither be created nor it can be destroyed but it can only be converted from one form to another.
Thus, we can conclude that in an exothermic chemical reaction, the energy gained by the surroundings must be equal to the energy lost by the reaction.
