Lanthanoids — Predicted 2026
AI-Predicted Question Angles for UPSC 2026
Consequences of Lanthanoid Contraction on Chemical Properties
highLanthanoid contraction is a fundamental concept. While its effect on atomic radii of 2nd/3rd transition series is well-known, questions might delve deeper into its impact on other chemical properties. For instance, how it affects the covalent character of bonds, the solubility of compounds, or the stability of complexes. A question could present a scenario asking to explain a trend in reactivity or basicity based on the contraction, requiring a nuanced understanding beyond just size reduction. This tests analytical application of the concept.
Identification of Specific Lanthanoid Ions with Unusual Oxidation States and their Reactivity
mediumNEET often tests exceptions and specific examples. While $Ce^{4+}$ and $Eu^{2+}$ are common, questions might focus on less common but still stable alternative oxidation states like $Sm^{2+}$, $Yb^{2+}$, $Tb^{4+}$, or $Pr^{4+}$. The question could ask to identify an ion that acts as a strong oxidizing agent (e.g., $Ce^{4+}$) or a strong reducing agent (e.g., $Eu^{2+}$) and link it to its electronic configuration and stability. This requires memorization of specific examples and understanding the redox implications of achieving stable $4f$ configurations.
Distinguishing Lanthanoids from Actinoids based on Key Properties
mediumGiven that both are f-block elements, a comparative question highlighting the differences between lanthanoids and actinoids is a strong possibility. Aspects like the range of oxidation states, radioactive nature, tendency for complex formation, and the extent of contraction (actinoid contraction being greater) are key differentiators. A question might present properties and ask to identify whether they belong to lanthanoids or actinoids, or to pick the incorrect distinguishing feature. This tests a broader understanding of the f-block elements as a whole.