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Assertion (A) : Actinoids… (Class 12 Chemistry 2026, Q15)

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ChemistryCBSE Class 12 · Board exam 2026, set 56/1/1 · 1 mark · Assertion-reason

CBSE Class 12 Chemistry 2026: question 15

Set in the CBSE Class 12 board exam of 2026, paper 56/1/1, 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-basedThe d- and f-Block Elements

Assertion (A) : Actinoids show wide range of oxidation states.
Reason (R) : Actinoids are radioactive in nature.

  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)Assertion (A) is false, but Reason (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 56/1/1.

Hints

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

Hint 1

Why do actinoids show variable oxidation states?

Hint 2

Does radioactivity affect the oxidation state?

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. Actinoids show a wide range of oxidation states because the 5f, 6d and 7s energy levels are close in energy. A is true.

  2. Actinoids are radioactive, so R is true, but radioactivity does not explain the oxidation states. Option (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Both statements are true but R does not explain A (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from The d- and f-Block Elements, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 56/1/1: 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.