CBSE 2025 · Region 7 · Set 2 · Q15 · 1 mark
Assertion (A) : Actinoids show irregularities in their electronic configurations.
Reason (R): This is due to varying stability of $\displaystyle \mathrm{f}^{0}, \mathrm{f}^{7}$ and $\displaystyle \mathrm{f}^{14}$ configurations.
Official answer
From CBSE’s own marking scheme for this paper.
(A)
Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
The d-and f-Block ElementsThe ActinoidsUnderstandassertion_reasonmedium
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CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.