1.

The lanthanide contraction is due to

Answer»

perfect shielding of F-orbitals
perfect shielding of d-orbitals
imperfect shielding of f-orbitals
imperfect shielding of d-orbitals

Solution :As we move from Ce to Lu, nuclear charge or effective nuclear charge increases by one unit at each ELEMENT because addition of 14-electrons in 4f-orbitals. The shielding EFFECT of 4f-electrons is very less or poor, which is due to diffused shape of 4f-orbital. The shielding effect of orbitals decreases in order.
`s gt p gt d gt f.`
Hence 4f-electrons are not able to shield perfectly the attraction between nucleus and outermost eletronic orbit.
The effect of INCREASED nuclear charge is more than that of shielding effect of 4f-orbitals. hence atomic or ionic size decreases from Ce to Lu.


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