Electronic Configuration — Predicted 2026
AI-Predicted Question Angles for UPSC 2026
Identification of Lanthanoids with $5d^1$ Configuration
highThe presence of a $5d^1$ electron in the ground state of Ce, Gd, and Lu is a classic exception and a frequently tested concept. Students often overlook this detail, assuming strict $4f$ filling. Questions will likely ask to identify which lanthanoids possess this feature or to provide the correct configuration for one of these specific elements. This tests both recall and understanding of stability factors.
Correlation between Electronic Configuration and Oxidation States
highNEET frequently assesses the ability to link electronic configuration to chemical properties, especially oxidation states. Expect questions asking why $Eu^{2+}$ and $Yb^{2+}$ are stable (due to $f^7$ and $f^{14}$ respectively), or why $Ce^{4+}$ is stable (due to $f^0$). Questions might also involve identifying the most stable non-$+3$ oxidation state for a given lanthanoid based on its configuration, or comparing the reducing/oxidizing power of different lanthanoid ions.
Magnetic Properties based on Unpaired Electrons
mediumThe number of unpaired electrons in the $4f$ subshell determines the magnetic properties (paramagnetism/diamagnetism). Questions could ask to identify a diamagnetic lanthanoid ion (e.g., $La^{3+}$, $Lu^{3+}$, $Ce^{4+}$) or to determine the number of unpaired electrons for a specific ion. This requires correctly deriving the ionic configuration and applying Hund's rule to the $f$-orbitals. While exact magnetic moment calculations are rare, qualitative comparisons are common.
Comparison with Actinoids or d-block elements
mediumA comparative question, highlighting the differences in electronic configuration between lanthanoids and actinides (e.g., $4f$ vs $5f$ filling, greater variability in actinoid oxidation states due to $5f-6d-7s$ energy proximity) or with d-block elements, is a plausible angle. This tests a broader understanding of periodic trends and f-block characteristics.