Final answer:
An exothermic reaction releases energy in the form of heat, and setting off a thermonuclear bomb is an example of such a reaction.
Step-by-step explanation:
An exothermic reaction releases energy in the form of heat. One example of an exothermic reaction is burning, which gives off heat into the surroundings. Another example is the formation of ice in a freezer, where heat is pulled out of the water and released into the surroundings. Setting off a thermonuclear bomb is an example of an exothermic reaction, as it releases a tremendous amount of heat into the environment.