Which of the following elements are exception | vedclass

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(C) The $(n + l)$ rule (also known as the Aufbau principle) states that electrons fill orbitals in order of increasing $(n + l)$ values.For $La$ $(Z=5

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Both $(a)$ and $(b)$

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(C) The $(n + l)$ rule (also known as the Aufbau principle) states that electrons fill orbitals in order of increasing $(n + l)$ values.For $La$ $(Z=57)$,the configuration is $[Xe] 5d^1 6s^2$. According to the $(n + l)$ rule,the $4f$ orbital $(n=4, l=3, n+l=7)$ should be filled before the $5d$ orbital $(n=5, l=2, n+l=7)$. However,the electron enters the $5d$ orbital instead of the $4f$ orbital.Similarly,for $Ac$ $(Z=89)$,the configuration is $[Rn] 6d^1 7s^2$. The electron enters the $6d$ orbital instead of the $5f$ orbital.Thus,both $La$ and $Ac$ are exceptions to the $(n + l)$ rule.

Which of the following elements are exceptions to the $(n + l)$ rule?

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