In any chemical reaction, the older chemical bonds are broken and the new chemical bonds are fond between different atoms or molecules. Hence, during the exothermic chemical reaction, the heat energy is released, which was stored in the older chemical bond. So, during the chemical reaction, these older bonds break and releases heat energy.
The correct answer is option A. The energy was stored in chemical bonds.
An exothermic reaction is a reaction that releases energy in form of light and heat to the surrounding. In any reaction, energy can not be created nor destroy but are transformed from one form to another. Therefore, before an exothermic reaction, the energy is stored in chemical bonds.