Which of the following factor may be regarded as the main cause of lanthanide contraction?A. Poor shielding of `4f`-electrons in compare to other electrons in the sub-shellB. Effective shielding of one of the `4f`-electrons by another in the sub-shellC. Poorer shielding of `5d` electron by `4f`-electrons.D. Greater shielding of `5d` electrons by `5f-electron.

Which of the following factor may be regarded as the main cause of lan

1.	Which of the following factor may be regarded as the main cause of lanthanide contraction?A. Poor shielding of `4f`-electrons in compare to other electrons in the sub-shellB. Effective shielding of one of the `4f`-electrons by another in the sub-shellC. Poorer shielding of `5d` electron by `4f`-electrons.D. Greater shielding of `5d` electrons by `5f-electron.
Answer» Correct Answer - A This phienomenon is associated with the intervention of the `4f` orbitals which must be filled before the `5d` series of elements begin The filling of `4f` before `5d` orbital results in a regular decrease in atomic radii called is lanthanoid contraction. This is because of poor shielding of one of the `4f`-electrons by another in the sub-shell.

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