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UPSC 2001: Consider the following statements: In a nuclear reactor, self-sustained chain reaction is possible, because I. more neutrons are released in each of the fission reactions. II. the neutrons immediately take part in the fission process. III. the fast neutrons are slowed down by Graphite. IV. every neutron released in the fission reaction initiates further fission. Which of these statements are correct?
(a)I, II and III
(b)I and III
(c)II and IV
(d)II, III and IV
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Not attemptedCorrect Answer: (b) I and III
A self-sustained chain reaction is possible because each fission of ²³⁵U releases several fast neutrons (statement I) and a moderator such as graphite slows these neutrons to thermal energies so they can trigger further fission (statement III). Neutrons do not ‘immediately’ take part in fission (II is not essential) and only a fraction—not every—neutron causes another fission (IV is wrong). Hence only I and III are correct. ([licchavilyceum.com](https://licchavilyceum.com/upsc-civil-services-prelims-2001-solved-question-paper/?utm_source=openai))
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Frequently Asked Questions
What is the correct answer to this UPSC 2001 Science & Technology question?▼
The correct answer is option (b): I and III. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Energy & Environment question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2001, GS Paper 1, as Question 106. It falls under Science & Technology > Energy & Environment.
What is the difficulty level of this UPSC question?▼
This question is rated "moderate". It requires sound conceptual understanding of the topic.
How many UPSC Prelims questions have been asked from Energy & Environment?▼
UPSC has asked 48 questions from Energy & Environment (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.