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(C) Lanthanoid contraction is the steady decrease in the atomic and ionic radii of lanthanoids with an increase in atomic number. This is primarily du

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Effective nuclear charge

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(C) Lanthanoid contraction is the steady decrease in the atomic and ionic radii of lanthanoids with an increase in atomic number. This is primarily due to the poor shielding effect of $4f$ electrons. As the atomic number increases,the nuclear charge increases by one unit at each step,but the additional electron enters the $4f$ orbital. Since $4f$ electrons have a very poor shielding effect,the effective nuclear charge experienced by the outer electrons increases,causing the electron cloud to be pulled closer to the nucleus,resulting in a decrease in size.

Lanthanoid contraction is caused due to an increase in . . . . . . .

Similar Questions

Assertion : Ionisation enthalpies of the early actinoids are lower than for early lanthanoids.
Reason : $5f$ electrons are more effectively shielded from nuclear charge than $4f$ electrons.

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$(a)$ Actinoid contraction increases from one element to the next.
$(b)$ Actinoid contraction decreases from one element to the next.
$(c)$ Lanthanoid contraction occurs,but actinoid contraction does not occur.

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