ANS:B - 2.5

When uranium-235 undergoes nuclear fission, it splits into two smaller nuclei, releasing a large amount of energy in the process. Along with this energy release, several neutrons are also emitted. These emitted neutrons are called "fast neutrons" because they have high kinetic energy. The average number of fast neutrons produced per fission event of uranium-235 is approximately 2.5. This means that, on average, each time a uranium-235 atom undergoes fission, it releases around 2.5 fast neutrons. These fast neutrons play a critical role in sustaining a nuclear chain reaction. If one of these fast neutrons encounters another uranium-235 atom, it can induce fission in that atom, releasing more neutrons and continuing the chain reaction. This process is fundamental in nuclear reactors for the generation of energy.