Answer : The correct option is, Chain reaction.
Explanation :
Transmutation : It is defined as the process where a nucleus is converted to another nucleus. Or we can say that the conversion of chemical elements into another.
Nuclear fusion : It is a process where the two small nuclei converted to form a heavy nuclei and release some energy.
Nuclear fission : It is a process where a heavier nuclei (unstable nuclei) converted into two or more small (stable nuclei) and release some energy.
Critical mass : It is the smallest mass of substance that will start a chain reaction in a nuclear reactor.
Chain reaction : It is a independent series of the reactions. The nuclear fission of uranium are the example of chain reaction.
In fission of uranium nucleus, three neutrons are produced. Then these fast moving neutrons undergo successive collision with the other uranium nuclei.
As more and more nuclei are decomposes by the neutrons, more and more neutrons are produced and an uncontrolled fission process is started which is known as chain reaction.
Hence, an ongoing series of fission reactions is called a, chain reaction.
