Which reaction (s) most likely release the greatest amount of energy

The reaction that is most likely to release the greast amount of energy is the nucleus. If that is what you are asking about. If not, then it might be Which of the following situations represent (s) a transformation of one type of energy to another?

1) the burning of gasoline in a car engine to move a car

2) the production of sugar by photosynthesis

3) the production of electrical power by damming a river

4) playing music by putting new batteries in your CD player

5) all of the above