Lanthanoid contraction is the:
ADecrease in valency
BShrinkage during cooling
CSteady decrease in atomic and ionic radii of lanthanoids from La (Z=57) to Lu (Z=71) — due to poor shielding of one 4f electron by another
DDecrease in the temperature of lanthanoid metals
Answer & Solution
Correct answer: C. Steady decrease in atomic and ionic radii of lanthanoids from La (Z=57) to Lu (Z=71) — due to poor shielding of one 4f electron by another
**Lanthanoid contraction**: as Z increases across the lanthanoid series, **4f electrons are added but their poor mutual shielding** means effective nuclear charge increases more than expected → **radii decrease gradually** from La (~187 pm) to Lu (~173 pm).
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