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Assertion (A): Nuclei… (Class 12 Physics SQP 2024-25, Q15)

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PhysicsCBSE Class 12 · Sample paper, session 2024-25 · 1 mark · Assertion-reason

CBSE Class 12 Physics sample paper 2024-25: question 15

From the official CBSE sample question paper for 2024-25, section A, question 15, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q15 · 1 mark · Assertion-reasonCompetency-basedNuclei

Assertion (A): Nuclei having mass number about 60 are least stable.
Reason (R): When two or more light nuclei are combined into a heavier nucleus then the binding energy per nucleon will decrease.

  1. (A)If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  2. (B)If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
  3. (C)If Assertion is true but Reason is false.
  4. (D)If both Assertion and Reason are false.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

Recall the shape of the BE/A curve.

Hint 2

Why does fusion release energy?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Nuclei with (such as Fe) have the maximum binding energy per nucleon, so they are the most stable. The Assertion is false.

    ½ mark

  2. In fusion of light nuclei, binding energy per nucleon increases, so the Reason is false too. The answer is (D).

    ½ mark

Answer: Option (D)

Where the marks are

  • A is false: A≈60 is most stable (0.5 mark)
  • R is false: fusion increases BE/nucleon (0.5 mark)

Revise the chapter

Practise this chapterBoard-style questions from Nuclei, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.