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Assertion (A): Total… (Class 12 Physics SQP 2025-26, Q13)

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PhysicsCBSE Class 12 · Sample paper, session 2025-26 · 1 mark · Assertion-reason

CBSE Class 12 Physics sample paper 2025-26: question 13

From the official CBSE sample question paper for 2025-26, section A, question 13, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q13 · 1 mark · Assertion-reasonCompetency-basedAtoms

Assertion (A): Total energy of an electron in hydrogen atom is negative.
Reason (R): The centripetal force is provided by electrostatic force.

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

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Why is the total energy negative?

Hint 2

Does knowing what provides the centripetal force by itself explain the sign?

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. The assertion is true: eV is negative because the electron is bound to the nucleus.

  2. The reason is true, since the Coulomb attraction provides the centripetal force. However, the negative sign comes from the energy being a bound state, not from that fact alone, so the reason is not the correct explanation. Option (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Judges both statements true but R not the explanation (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Atoms, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2025-26: 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.