Periodic Trends in Properties — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Periodic Trends in Properties.

Comparative Ionization Enthalpy (IE) with Exceptions

high

NEET consistently tests the exceptions to the general IE trend. Questions comparing IE of Group 2 vs. Group 13 elements (e.g., Mg vs. Al) or Group 15 vs. Group 16 elements (e.g., N vs. O) are highly probable. Students must understand the stability associated with fully-filled (ns$^2$) and half-filled (np$^3$) subshells. A question asking to arrange a mixed set of elements (e.g., Na, Mg, Al, Si, P, S) by their first or second ionization enthalpy is very likely.

Ordering of Isoelectronic Species by Size

high

This is a fundamental concept and a favorite for NEET. Questions will provide a list of isoelectronic ions (e.g., O$^{2-}$, F$^-$, Na$^+$, Mg$^{2+}$) and ask for their arrangement in increasing or decreasing order of ionic radius. The key is to identify the number of electrons and then compare nuclear charges. This tests a clear, unambiguous rule.

Electron Gain Enthalpy (EGE) with F vs. Cl Exception

medium

The anomaly where chlorine has a more negative electron gain enthalpy than fluorine is a classic exception often tested. Questions might directly ask for the reason or include F and Cl in an ordering question for EGE. Understanding the role of electron-electron repulsion in small atoms is crucial here. Questions might also involve elements with positive EGE (noble gases, Group 2, Group 15).

Acidic/Basic/Amphoteric Nature of Oxides

medium

Predicting the nature of oxides based on the element's position is a recurring theme. Questions might provide a list of oxides and ask to identify the amphoteric one, or to arrange them in order of increasing acidity/basicity. Knowledge of common amphoteric oxides (Al$_2$O$_3$, ZnO, PbO, SnO$_2$) is important.

Impact of Lanthanide Contraction

low

While less frequent, questions on lanthanide contraction and its consequences (e.g., similar atomic radii of 4d and 5d transition elements, similar properties of Zr/Hf) can appear. This tests a deeper understanding of the f-block elements' influence on subsequent d-block elements. It's a slightly more advanced concept but within the NEET syllabus.