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The shape of f-orbitals is very much diffused and they have poor shielding effect. The effective nuclear charge increases due to imperfect shielding of one electron by another in the same subshell which causes the contraction in the size of electron charge cloud. This contraction in size is known as lanthanoid contraction.

1. The shape of f-orbitals is very much diffused and they have poor shielding effect.
2. The effective nuclear charge increases due to imperfect shielding of one electron by another in the same subshell which causes the contraction in the size of electron charge cloud. This contraction in size is known as lanthanoid contraction.
3. The effective nuclear charge decreases due to perfect shielding of one electron by another in the same subshell which causes the expansion in the size of electron charge cloud.
4. The effective nuclear charge increases due to perfect shielding of one electron by another in the same subshell which causes the contraction in the size of electron charge cloud.

Correct answer: The effective nuclear charge increases due to imperfect shielding of one electron by another in the same subshell which causes the contraction in the size of electron charge cloud. This contraction in size is known as lanthanoid contraction.

Solution

The lanthanoid contraction occurs due to the poor shielding effect of f-orbitals, leading to an increase in effective nuclear charge and a contraction in atomic size. Option B correctly describes this phenomenon.

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