Atomic Radius and Ionic Radius — Predicted 2026
AI-Predicted Question Angles for UPSC 2026
Comparison of isoelectronic species with varying charges and periods.
highIsoelectronic species are a perennial favorite in NEET, as they test the fundamental understanding of how nuclear charge affects electron cloud size when the number of electrons is constant. Future questions will likely continue to present a mix of cations and anions from different periods that share the same electron configuration, requiring students to rank them by size. For example, comparing $S^{2-}$, $Cl^-$, $K^+$, $Ca^{2+}$ (all 18 electrons) or $N^{3-}$, $O^{2-}$, $F^-$, $Na^+$, $Mg^{2+}$, $Al^{3+}$ (all 10 electrons) is a high-probability question type.
Combined trends: Comparing elements from different periods and groups.
mediumWhile direct period/group trends are common, NEET might pose more challenging questions that require combining both trends. For instance, comparing an element from the bottom of one group with an element from the top of an adjacent group, or comparing a cation from one period with an anion from another. This tests a more holistic understanding of the periodic table and the interplay of nuclear charge, number of shells, and electron-electron repulsion. For example, comparing $Li^+$, $Mg^{2+}$, $Al^{3+}$ and $F^-$, $Cl^-$, $Br^-$. Such questions require careful step-by-step analysis.
Conceptual questions on the factors influencing radii, including shielding effect and effective nuclear charge.
mediumBeyond just stating trends, NEET increasingly focuses on the 'why' behind them. Questions might ask to identify the primary reason for a particular trend (e.g., why atomic radius decreases across a period) or to explain the role of the shielding effect (especially for d-block elements or lanthanides). Understanding effective nuclear charge ($Z_{eff}$) and how it's influenced by shielding will be key. These questions often come in the form of 'Assertion-Reason' or 'Which statement is correct/incorrect' types.