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Classification of Elements and Periodicity in Properties appeared 36 times across 3 years — 4.2% of Chemistry. This question is from Periodic Trends in Atomic Radii.

Year 2026 2025 2024 Total
Questions 9 16 11 36
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The type of oxide formed by the element among Li, Na, Be, Mg, B and Al that has the least atomic radius is: (1) A₂O₃ (2) AO₂ (3) AO (4) A₂O

Solution & Explanation

Core Logic

Let's analyze the periodic trend among the listed elements: Li, Na, Be, Mg, B, Al.

  • Atomic radius decreases across a period due to increasing effective nuclear charge (Zeff).
  • Atomic radius increases down a group due to addition of electron shells.

    • Comparing Period 2 elements (Li, Be, B): Boron (B) has the highest atomic number here and thus the smallest atomic radius. Boron forms an oxide where its oxidation state is +3, which gives B₂O₃. This matches the structural template A₂O₃.

Pattern Recognition

Smallest element in Period 2 (excluding noble gases) is on the far right. Boron belongs to Group 13, so it forms traditional trivalent acidic oxides (A₂O₃).

Chapter Mix

Class 11 Chemistry: Classification of Elements and Periodicity in Properties

Reference Study Guides

Classification Of Elements And Periodicity In Properties

More Classification of Elements and Periodicity in Properties Previous-Year Questions — Page 8

Q70 jee_main_2024_31_jan_morning Electron Gain Enthalpy
The correct sequence of electron gain enthalpy of the elements listed below is A. Ar B. Br C. F D. S Choose the most appropriate from the options given below:
  • A. C > B > D > A
  • B. A > D > B > C
  • C. A > D > C > B
  • D. D > C > B > A

Solution

Core Logic

Electron gain enthalpy (ΔegH) values are considered with their signs when ordering from largest to smallest algebraically.

ElementΔegH (kJ/mol)
F-333
S-200
Br-325
Ar+96

Arranging these algebraically from highest to lowest: +96 > -200 > -325 > -333 Thus, Ar > S > Br > F, which corresponds to A > D > B > C.

Pattern Recognition

Noble gases always have positive electron gain enthalpies (highest algebraically). Halogens have highly negative values (lowest algebraically). Fluorine is highly negative, Bromine is slightly less negative. Sulfur sits in between.

Chapter Mix

Class 11 Chemistry: Classification of Elements and Periodicity in Properties

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JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)