Question

which feature of nuclear fission reactions allows these reactions to take place in a chain reaction?
thermal energy is released and heats up the reactants.
more smaller atoms form that can undergo fission.
a larger atom is formed, which can then be split.
neutrons start the reaction and are released during it.

Explanation:

• In nuclear fission, a neutron starts the fission reaction (e.g., \(n + ^{235}U

ightarrow\) products).

• During the fission process, more neutrons are released (e.g., \(^{235}U + n

ightarrow ^{92}Kr+^{141}Ba + 3n\)).

• These released neutrons can then go on to cause fission in other \(^{235}U\) (or other fissile nuclei) atoms, creating a chain reaction.
• Thermal energy release (first option) is a by - product but not what drives the chain reaction.
• Smaller atoms formed (second option) are fission products and not usually fissile in the context of a typical nuclear fission chain reaction (e.g., \(^{92}Kr\) and \(^{141}Ba\) in the above example are not fissile).
• A larger atom is not formed in fission (third option is incorrect as fission is the splitting of a large nucleus).

Answer:

Neutrons start the reaction and are released during it.