JEE Main · 2019 · 10 Jan 2019 · Shift 1 · d and f Block Elements

The effect of lanthanoid contraction in the lanthanoid series of elements by the large means

(A)increase in both atomic and ionic radii
(B)decrease in atomic radii and increase in ionic radii
(C)decrease in both atomic and ionic radii✓ Correct
(D)increase in atomic radii and decrease in ionic radii

Answer: (C)

Solution

Across the lanthanoid series the added

4 f

electrons shield the growing nuclear charge poorly, so the effective pull on the outer electrons creeps up and the size steadily shrinks. This steady shrinkage, the lanthanoid contraction, shows up in both the neutral atoms and their ions, so atomic and ionic radii both decrease along the series.

JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Single correct option

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