Answer the following question given this paragraph: 

Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. It begins when the nucleus of a radioactive atom gains a neutron.


Q: What term describes the splitting of the nucleus of an atom into two smaller nuclei?

 Choices:

- nuclean fusion

- atomic reaction

- critical fission

- nuclear fission

A:
nuclear fission
