Consider the following statements: In a nuclear reactor, self-sustained chain reaction is possible, because

1. more neutrons are released in each of the fission reactions.
2. the neutrons immediately take part in the fission process.
3. the fast neutrons are slowed down by Graphite.
4. every neutron released in the fission reaction initiates further fission.

Which of these statements are correct?

1. I, II and III
2. I and III
3. II and IV
4. II, III and IV

Explanation

Option (b) is correct

• In a nuclear reactor, a self-sustained chain reaction is possible because each fission reaction releases additional neutrons, making Statement I correct. These neutrons are initially fast-moving and are slowed down by moderators such as Graphite to increase the probability of further fission, so Statement III is also correct. Statement II is incorrect because neutrons do not immediately take part in fission; they usually need to be slowed down first. Statement IV is also incorrect because not every neutron released causes another fission—some may escape or get absorbed without producing further reactions.

Answer: (b) I and III