An endothermic reaction is one that uses which form of energy?
nuclear fusion
electrical energy
chemical engery
sound energy

The answer is an chemical energy since the endothermic reaction is any chemical reaction that absorbs heat from its environment. The absorbed energy provides the activation energy for the reaction to occur and results in a net decrease in temperature because absorbed heat from the surroundings is stored in form of the energy in the bonds formed in the reaction.

the correct choice is a .

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it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me