Variation in Atomic and Ionic Sizes — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Variation in Atomic and Ionic Sizes.

Direct application of lanthanoid contraction consequences.

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NEET frequently tests the direct consequences of lanthanoid contraction. Students should be prepared for questions asking which pair of elements has similar sizes (e.g., Zr/Hf, Nb/Ta), or why 5d elements are denser than 4d elements, or why 4d and 5d elements in the same group exhibit similar chemical properties. These are fundamental applications of the concept and are easily framed as MCQs.

Ordering of atomic/ionic radii involving multiple factors.

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Questions requiring the arrangement of a set of atoms or ions in increasing or decreasing order of size are common. These questions often combine trends across a period, down a group, and the effect of oxidation state on ionic radius. For transition elements, this might involve comparing $M^{2+}$ ions across a series or comparing an atom with its ions, or even comparing a 3d element with its 4d/5d congener, requiring careful consideration of all influencing factors.

Conceptual understanding of factors influencing size in transition series.

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Beyond just knowing the trends, NEET can probe the 'why' behind the trends. Questions might ask about the primary reason for the initial decrease, the near constancy in the middle, or the slight increase at the end of a transition series. This requires a clear understanding of the interplay between effective nuclear charge, shielding effect (especially poor shielding by d-electrons), and electron-electron repulsion.