- The fission of a uranium atom refers to the process in which the nucleus of the uranium atom splits into two smaller nuclei, releasing a significant amount of energy.
- In the fission process, the uranium-235 isotope is commonly used. When a uranium-235 atom undergoes fission, it can produce different combinations of daughter nuclei, along with the release of several neutrons.
- The average number of neutrons released per fission event is a critical factor in determining the sustainability and efficiency of a nuclear chain reaction.
- The correct answer is option 'C' which states that the average number of neutrons released by the fission of one uranium atom is 2.5.

Explanation:
- In a nuclear fission reaction, the uranium-235 nucleus absorbs a slow-moving neutron, becoming highly unstable.
- The uranium-235 nucleus then splits into two smaller nuclei, referred to as fission fragments, along with the release of energy.
- Along with the fission fragments, two to three neutrons are typically released as well.
- These released neutrons can then go on to collide with other uranium-235 nuclei, causing them to undergo fission and release more neutrons.
- This process creates a chain reaction, where each fission event triggers subsequent fission events.
- The average number of neutrons released per fission event is determined by the number of neutrons that go on to cause additional fission events.
- In the case of uranium-235, on average, each fission event releases 2.5 neutrons, leading to the sustainment of a chain reaction.
- The actual number of neutrons released can vary slightly depending on various factors, such as the energy of the incident neutron and the specific fission products produced.
- The control of the number of neutrons released per fission event is crucial in nuclear reactors, as it determines the rate of the chain reaction and prevents the reactor from becoming unstable or uncontrollable.

In conclusion, the average number of neutrons released by the fission of one uranium atom is 2.5. This value is important in maintaining a sustainable and controlled chain reaction in nuclear reactors.