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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 Atomic Radii Trends.

Year 2026 2025 2024 Total
Questions 9 16 11 36
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Choose the incorrect trend in the atomic radii (r) of the elements:

Solution & Explanation

Related Formula
Atomic Radius (r) ∝ 1Zeff (Across a period) Atomic Radius (r) ∝ Number of Shells (n) (Down a group)
Core Logic

Let's review the periodic table positioning and trends:

  • Across a period from left to right, effective nuclear charge (Zeff) increases, drawing electrons closer to the nucleus. Hence, atomic radius decreases.
  • Mg and Al sit in Period 3. Since Al is further to the right (Z=13) than Mg (Z=12), the radius of Al is smaller than that of Mg:
rMg > rAl

Thus, the stated trend rMg < rAl is incorrect.

Step 1: Cross-Checking Valid Trends
  • rBr < rK: Correct, as potassium sits at the start of Period 4, bromine sits near the end.
  • rRb < rCs: Correct, atomic size increases down Group 1.
  • rAt < rCs: Correct, cesium sits far below and left compared to astatine.
Pattern Recognition

Period 3 size ranking baseline: Na > Mg > Al > Si > P > S > Cl. Moving rightward always drops the radius size unless noble gas van der Waals constraints interfere.

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%)