The correct option is B Atavism
Radiation is the energy which is coming from a source. It is in the form of high-speed particles or rays.
Atavism is the sudden reappearance of ancestral traits after several generations.
A human baby born with a tail and coarse hair like vertebrates which has disappeared in recent generations represents the case of atavism.
Mutations are the changes in the nucleotide sequences of the genetic material. Mutations may arise due to radiations, chemical mutagens, oncogenes etc.
Crossing over is the exchange of genetic material between non-sister chromatids. This results in variations. It occurs during cell division.
b. Atavism