The correct answer is option 4 i.e. Nuclear fusion reaction.
Nuclear fusion reactions are the source of energy in the Sun and other stars.
It takes considerable energy to force the nuclei to fuse. The conditions needed for this process are extreme – millions of degrees of temperature and millions of pascals of pressure.
Nuclear fusion
Fusion means joining lighter nuclei to make a heavier nucleus, most commonly hydrogen or hydrogen isotopes to create helium, such as
It releases a tremendous amount of energy, according to the Einstein equation, as the mass of the product is little less than the sum of the masses of the original individual nuclei.
Chemical reactions
The transformation of chemical substances (known as reactants) into a new chemical substance (known as products) by making and breaking of chemical bonds between different atoms of reactants sometimes in presence of a catalyst (which changes the rate of reaction) is known as Chemical Reaction.
Combustion Reaction
A chemical reaction between substances, usually including oxygen and usually accompanied by the generation of heat and light in the form of flame. Combustion reactions must involve 2 as one reactant.
Many combustion reactions occur with a hydrocarbon, a compound made up solely of carbon and hydrogen. The products of the combustion of hydrocarbons are carbon dioxide and water.
Nuclear fission
In a process called nuclear fission, the nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low-energy neutrons, can be split apart into lighter nuclei.
When this is done, a tremendous amount of energy is released if the mass of the original nucleus is just a little more than the sum of the masses of the individual products.
The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a self sustaining fission chain reaction that releases energy at a controlled rate.
The released energy can be used to produce steam and further generate electricity.