I don't want to just do your homework for you, so I'll explain the phenomena below and let you work out the answers based on that.
A chemical reaction, like combustion or rusting, is not a nuclear reaction (neither fission nor fusion). Only the electrons surrounding the nuclei are involved, not the nuclei themselves.
When large nuclei like plutonium and uranium split - either in a controlled way in a nuclear power point or in an uncontrolled way in a nuclear weapon - what is happening is nuclear fission. 'Fission' just means splitting or breaking apart. It's what they used to mean when they talked about 'splitting the atom'.
When small nuclei like hydrogen and helium join together to produce larger nuclei, nuclear fusion is taking place. 'Fusion' means melting together or joining together.