7.18 understand that the fission of U-235 produces two daughter nuclei and a small number of neutrons

In nuclear fission, a slow moving neutron gets absorbed by the nucleus of an U-235 atom. This causes the atom to split. The nucleus will split into two smaller 'daughter' nuclei and will also 'spit out' a small number of neutrons.

NOTE: When uranium-235 splits into two daughter cells, these cells will be radioactive as they will have the 'wrong' number of neutrons in them. They will also be lighter elements than uranium.