Q.98 Chemistry · Section B ⭐ 360° Option Elimination Active
NEET 2024 Chemistry Question 98 Solution
Topic: The d- and f-Block Elements · Official NTA Booklet Code T1
Question
— The pair of lanthanoid ions which are diamagnetic is
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Verified Against NTA Final Answer Key
Option (3) : Ce4+ and Yb2+
📚 The d- and f-Block Elements Easy
📋 Given Parameters & Problem Setup
Target property Diamagnetic lanthanoid ions (unpaired electrons n = 0)
Elements involved Cerium (Ce, Z=58), Ytterbium (Yb, Z=70), Gadolinium (Gd, Z=64), Europium (Eu, Z=63)
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⏱️ Save ~35 seconds The 30-Second Exam Hall Shortcut: ⚡ Empty 4f0 and Filled 4f14 Diamagnetism Hack
Lanthanoid ions are diamagnetic ONLY when 4f is completely EMPTY (4f⁰, e.g. Ce⁴⁺, La³⁺) or completely FILLED (4f¹⁴, e.g. Yb²⁺, Lu³⁺)! Ce⁴⁺ and Yb²⁺ is the only diamagnetic pair!
1 Diamagnetic requires zero unpaired electrons: n = 0.
2 In lanthanoids, this occurs exclusively with 4f⁰ (noble gas [Xe] core) or 4f¹⁴ (completely filled f-subshell).
3 Check Ce⁴⁺: Ce is [Xe] 4f¹ 5d¹ 6s². Losing 4 electrons leaves [Xe] 4f⁰ -> n = 0 (DIAMAGNETIC).
4 Check Yb²⁺: Yb is [Xe] 4f¹⁴ 6s². Losing 2 valence 6s electrons leaves [Xe] 4f¹⁴ -> n = 0 (DIAMAGNETIC).
5 Both Ce⁴⁺ and Yb²⁺ have zero unpaired f-electrons and are diamagnetic.
6 Other ions have unpaired f-electrons (e.g. Gd³⁺ has 4f⁷, Eu²⁺ has 4f⁷, Eu³⁺ has 4f⁶).
7 Option (3) in 5 seconds!
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Why You Can 100% Trust This Shortcut: NCERT Chemistry · The d- and f-Block Elements (Lanthanoids: electronic configurations, oxidation states, and magnetic properties: Ce4+ [4f0] and Yb2+ [4f14] are diamagnetic).
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Electronic Configurations of Lanthanoids
Lanthanoids have valence electrons filling the 4f subshell, with neutral ground states: - Cerium (Ce, Z = 58): [Xe] 4f¹ 5d¹ 6s² - Ytterbium (Yb, Z = 70): [Xe] 4f¹⁴ 6s² - Europium (Eu, Z = 63): [Xe] 4f⁷ 6s² - Gadolinium (Gd, Z = 64): [Xe] 4f⁷ 5d¹ 6s²
Step 2
Determining Configurations and Unpaired Electrons of Cations
Removing electrons from the outermost orbitals: 1. Ce⁴⁺: Loses 6s², 5d¹, and 4f¹ ⟹ [Xe] 4f⁰. Possesses an empty 4f subshell (n = 0 unpaired electrons) ⟹ Diamagnetic. 2. Yb²⁺: Loses 6s² ⟹ [Xe] 4f¹⁴. Possesses a completely filled 4f subshell (n = 0 unpaired electrons) ⟹ Diamagnetic. 3. Gd³⁺: Loses 6s² and 5d¹ ⟹ [Xe] 4f⁷ (n = 7 unpaired electrons) ⟹ Strongly paramagnetic. 4. Eu³⁺: Loses 6s² and one 4f ⟹ [Xe] 4f⁶ (n = 6 unpaired electrons) ⟹ Paramagnetic. 5. Eu²⁺: Loses 6s² ⟹ [Xe] 4f⁷ (n = 7 unpaired electrons) ⟹ Paramagnetic.
Step 3
Conclusion
Ce⁴⁺ (4f⁰) and Yb²⁺ (4f¹⁴) both possess zero unpaired f-electrons. Consequently, both are diamagnetic, matching Option (3).
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 (1)
✗ Incorrect Verdict & Scientific Reason:
Gd3+ has 7 unpaired electrons (4f7); Eu3+ has 6 unpaired electrons (4f6). Both are paramagnetic.
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Student Fallacy (Why candidates pick this trap): Confusing half-filled stability with diamagnetism.
2 (2)
✗ Incorrect Verdict & Scientific Reason:
Pm3+ is 4f4 (n=4) and Sm3+ is 4f5 (n=5). Both are paramagnetic.
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Student Fallacy (Why candidates pick this trap): Random selection.
3 (3)
✓ 100% Correct Verdict & Scientific Reason:
Ce4+ is 4f0 and Yb2+ is 4f14; both have zero unpaired electrons and are diamagnetic.
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Why this is airtight: None.
4 (4)
✗ Incorrect Verdict & Scientific Reason:
Ce3+ is 4f1 (n=1) and Eu2+ is 4f7 (n=7). Both are paramagnetic.
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Student Fallacy (Why candidates pick this trap): Confusing Ce3+ with Ce4+.
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NTA Trap Alert: Confusing Half-Filled 4f7 (Gd3+) with Diamagnetism
Students frequently associate "extra stability" of half-filled 4f7 with diamagnetism. 4f7 has SEVEN unpaired electrons, making it the MOST paramagnetic ion, not diamagnetic!
🛡️ How to avoid the -1 mark: Diamagnetic means NO unpaired electrons: only 4f⁰ or 4f¹⁴.
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Core NEET Syllabus Standard
Chemistry Core Inorganic Chemistry · The d- and f-Block Elements Standard Benchmark
Core Scientific Principle Tested:
"Lanthanoid ions are diamagnetic only when they possess empty (4f0, e.g. Ce4+, La3+) or completely filled (4f14, e.g. Yb2+, Lu3+) f-orbitals."
Syllabus Focus: Lanthanoids: Electronic Configurations, Oxidation States, and Magnetic Properties
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
Empty zero (Ce4+) and full fourteen (Yb2+): the only diamagnetic lanthanoids seen!
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