None of the descriptions you provided accurately describe nuclear fusion. Here is the correct description of nuclear fusion:
Nuclear fusion is a process in which two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy in the process. This typically occurs at very high temperatures and pressures, such as those found in stars.
The statements you listed appear to describe nuclear fission instead, which involves a larger atom (typically a heavy nucleus) splitting into two smaller atoms, often after being hit by a neutron.