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Assertion (A) : Energy is… (Class 12 Physics 2026, Q15)

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PhysicsCBSE Class 12 · Board exam 2026, set 55/5/1 · 1 mark · Assertion-reason

CBSE Class 12 Physics 2026: question 15

Set in the CBSE Class 12 board exam of 2026, paper 55/5/1, 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) : Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.
Reason (R) : For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei, it decreases with increasing Z.

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

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/5/1.

Hints

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

Hint 1

Recall the shape of the BE/A versus A curve.

Hint 2

Check which way the curve slopes at each end.

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. Fission of heavy nuclei and fusion of light nuclei both increase the binding energy per nucleon, so energy is released. A is true.

  2. R has the trend reversed: binding energy per nucleon decreases with mass number for heavy nuclei and increases for light nuclei. So R is false.

    1 mark

Answer: Option (C)

Where the marks are

  • A true, R false because the trend is reversed (1 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 paper2026 board paper, set 55/5/1: 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.