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CBSE Class 12 · 2006 · Delhi Compartment · d and f Block ElementsShort Answer

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What is meant by lanthanoid contraction? State one use each of lanthanoid metals and of their oxides.

Solution

Lanthanoid contraction — the regular decrease in atomic and trivalent ionic radii across the lanthanoid series (La → Lu), caused by imperfect shielding of the nuclear charge by 4f electrons.
Use of lanthanoid metals: as mischmetal (Ln + Fe) in lighter flints and in magnesium alloys for bullets/shells.
Use of lanthanoid oxides: as phosphors in television/monitor screens (also as petroleum-cracking catalysts and glass-polishing agents).

CBSE Class 12 Board · 2006 · Delhi Compartment · Subjective

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  2. Assertion (A): Zr and Hf have almost similar atomic radii.
    Reason (R): This is due to lanthanoid contraction.
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  3. Which of the following ions has the electronic configuration 3d? (Atomic numbers: Mn = 25, Co = 27, Ni = 28)
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  4. Which property of transition metals enables them to behave as catalysts?
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