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Assertion (A) : Zr and Hf… (Class 12 Chemistry 2024, Q13)

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ChemistryCBSE Class 12 · Board exam 2024, set 56/5/1 · 1 mark · Assertion-reason

CBSE Class 12 Chemistry 2024: question 13

Set in the CBSE Class 12 board exam of 2024, paper 56/5/1, 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-basedThe d- and f-Block Elements

Assertion (A) : Zr and Hf are of almost similar atomic radii.
Reason (R) : This is due to Lanthanoid contraction.

  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 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 2024 board paper, set 56/5/1.

Hints

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

Hint 1

Hf comes immediately after the lanthanoid series.

Hint 2

Consider how poorly 4f electrons shield the nucleus.

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. Zr (160 pm) and Hf (159 pm) have nearly equal atomic radii.

  2. This is because the poorly shielding 4f electrons filled before Hf cause the lanthanoid contraction. Both statements are true and R explains A, so the answer is option (A).

    1 mark

Answer: Option (A)

Where the marks are

  • Both statements true and R is the correct explanation (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 paper2024 board paper, set 56/5/1: 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.