The correct answer is (a) controlled fusion reaction.
A hydrogen bomb is a thermonuclear weapon, a nuclear weapon that uses the heat of a nuclear fission reaction to initiate fusion reactions in a secondary stage. Fusion is the process that powers active stars, the hydrogen bomb is the only man-made device that can release energy from fusion reactions.
A fission reaction is a nuclear reaction in which an atomic nucleus splits into two or more smaller nuclei. The difference in mass between the reactants and products is manifested as the release of large amounts of energy. Fission is the process that powers nuclear reactors and nuclear weapons.
A controlled fusion reaction is a nuclear fusion reaction that is carried out in a controlled manner. This is in contrast to an uncontrolled fusion reaction, which is a nuclear fusion reaction that occurs spontaneously. Controlled fusion reactions are the subject of much research, as they have the potential to provide a clean and safe source of energy.
An uncontrolled fusion reaction is a nuclear fusion reaction that occurs spontaneously. This is in contrast to a controlled fusion reaction, which is a nuclear fusion reaction that is carried out in a controlled manner. Uncontrolled fusion reactions are the basis for the hydrogen bomb.