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Question: Answered & Verified by Expert
The main reason for larger number of oxidation states exhibited by the actinoids than the corresponding lanthanoids is:
Chemistryd and f Block ElementsNEETNEET 2005
Options:
  • A more energy difference between $5 f$ and $6 d$ orbitals than between $4 f$ and $5 \mathrm{~d}$ orbitals
  • B lesser energy difference between $5 \mathrm{f}$ and $6 \mathrm{~d}$ orbitals than between $4 f$ and $5 \mathrm{~d}$ orbitals
  • C larger atomic size of actinoids than the lanthanoids
  • D greater reactive nature of the actinoids than the lanthanoids
Solution:
1778 Upvotes Verified Answer
The correct answer is: lesser energy difference between $5 \mathrm{f}$ and $6 \mathrm{~d}$ orbitals than between $4 f$ and $5 \mathrm{~d}$ orbitals
In actinides, both $4 f$ and $5 f$ orbitals are present. These orbitals poorly shields the nuclear charge due to which the energy difference between the $5 f$ and the $6 d$ orbitals will be very low due to which the actinides will show a large number of oxidation states.
Caution
The elements in which the extra electron enters 5 - orbitals of $(n-2)^{\text {th }}$ shell (5f-block elements, actinides) shows the maximum oxidation state i.e. +7.

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