Concept:In the 3d transition series, chromium (\(Cr\)) and copper (\(Cu\)) exhibit anomalous electronic configurations to achieve the extra thermodynamic stability associated with half-filled and fully-filled d-subshells.
Solution:- Chromium (\(Z = 24\)): The expected configuration is \([Ar] \; 3d^4 \; 4s^2\). However, one \(4s\) electron promotes to the \(3d\) orbital to yield \([Ar] \; 3d^5 \; 4s^1\), achieving a stable half-filled \(3d\) subshell.
- Copper (\(Z = 29\)): The expected configuration is \([Ar] \; 3d^9 \; 4s^2\). It promotes one electron to form \([Ar] \; 3d^{10} \; 4s^1\), achieving a stable fully-filled \(3d\) subshell.
Why other options are incorrect:- Scandium (\(Sc\)) and Zinc (\(Zn\)) follow the standard Aufbau principle without any anomalous shifts.
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