a chain reaction that is caused by nuclear fission\na chain reaction that is caused by nuclear fusion\na…

Brief Explanations:

The image shows uranium - 235 ($^{235}$U) undergoing a process where it splits and releases neutrons which cause further splitting of other uranium - 235 nuclei. This is the characteristic of a chain reaction in nuclear fission. Nuclear fission releases energy as heavy nuclei break into lighter ones. Nuclear fusion involves the combination of light nuclei.

Answer:

A. a chain reaction that is caused by nuclear fission