Question

Ionization energy decreases as we move down the group. But moving down from the second to the third transition series ionization energy increases except for Y to La. This is due to:lanthanide contractionchange in the electronic configurationall of the abovepoor screening of d-electrons

Solution

The correct option is A lanthanide contractionDue to Lanthanide contraction, the ionization energy increases from the second to the third transition series. Lanthanide contraction is due to the poor shielding of  4f electrons.

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