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Transition and Inner Transition Elements — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryTransition and Inner Transition Elements2 Marks
Question
Why does lanthanum form $La ^{3+}$ ion, while cerium forms $Ce ^{4+}$ ion? $($Atomic number $La =57$ and $Ce$ $=58.)$
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Answer

$1.$ Electronic configuration Lanthanum is $La [Xe] 4f^\circ 5d^1 6s^2.$ By losing three electrons, $La$ acquires stable electronic configuration of $Xe$ and forms $La^{3+}.$
$2.$ Electronic configuration of Cerium is $Ce [Xe] 4f^1 5d^1 6s^2.$ By losing four electrons, $Ce$ acquires stable electronic configuration of $Xe$ and forms $Ce^{4+}.$

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