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D and F Block Elements question

2019 · 12 Apr · Shift 2 · Q12
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D and F Block Elements question

2019 · 12 Apr · Shift 2 · Q12

JEE MainChemistryD and F Block ElementsMCQ+4 / −1
The pair that has similar atomic radii is :
  1. A
    Mo and W
  2. B
    Mn and Fe
  3. C
    Ti and Hf
  4. D
    Sc and Ni
View written solutionFree

Correct answer: A

  1. Key concept: Lanthanoid contraction

    In the transition series, atomic radii usually decrease across a period.

    However, due to lanthanoid contraction, the atomic radii of many 5d elements become very close to those of their corresponding 4d elements.

    This happens because the poor shielding by 4f4f4f electrons causes a greater effective nuclear charge in the 5d series, contracting their size.

  2. Check each option

    Option A: Mo and W

    • Mo is a 4d element.
    • W is a 5d element and lies below Cr-group element.
    • Because of lanthanoid contraction, Mo and W have nearly similar atomic radii.
    • So, this option is correct.

    Option B: Mn and Fe

    • Both are in the same period (3d series).
    • Across a period, atomic radius decreases from left to right.
    • Hence Fe is smaller than Mn, so they are not especially similar.
    • Incorrect.

    Option C: Ti and Hf

    • Ti is a 3d element, Hf is a 5d element.
    • Hf is similar in size to Zr (because of lanthanoid contraction), not Ti.
    • So Ti and Hf do not have similar radii.
    • Incorrect.

    Option D: Sc and Ni

    • Both are in the 3d series, but the radius decreases significantly from Sc to Ni.
    • So they are not similar.
    • Incorrect.

  3. Conclusion

    The pair with similar atomic radii is: Mo and W\boxed{\text{Mo and W}}Mo and W​

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