Which type of reaction does this diagram represent?

1. A small ball impacts an atom of U 235, which blows apart into 3 small balls. 2. The first heads toward an atom of U 238, which has an arrow pointing to an X. The third heads toward an arrow pointing to an X. The second heads to an atom of U 235, where another explosion produces 2 small balls. 3. Each heads to atoms of U 235. The left one blows apart, creating 3 small balls heading away; the right blows apart creating 2 small balls heading away.
a chain reaction that is caused by nuclear fission
a chain reaction that is caused by nuclear fusion
a decrease in energy that is caused by nuclear fission
an increase in energy that is caused by nuclear fusion