Q.58 Chemistry ⭐ 360° Option Elimination Active

NEET 2026 Chemistry Question 58 Solution

Topic: Coordination Compounds · Official NTA Booklet Code 50

Question

According to crystal field theory, the correct order of ligands with respect to their decreasing order of field strength is

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Verified Against NTA Final Answer Key

Option (1) : CO > NH₃ > H₂O > Cl⁻

📚 Coordination Compounds Easy

📋 Given Parameters & Problem Setup

Theory Crystal Field Theory (CFT)

Ligands CO, NH₃, H₂O, Cl⁻

Required Order Decreasing order of crystal field strength (Δ_o)

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The 30-Second Exam Hall Shortcut: ⚡ Donor Atom Hierarchy Rule: C > N > O > Halogen

⏱️ Save ~45 seconds

Carbon donors are strongest; Halogens are weakest! Order: C > N > O > Halogen!

1 Recall ligand donor atoms: CO (Carbon donor), NH₃ (Nitrogen donor), H₂O (Oxygen donor), Cl⁻ (Halogen donor).

2 Spectrochemical field strength follows donor electronegativity and π-effects: C-donors > N-donors > O-donors > Halide ions.

3 Therefore: CO > NH₃ > H₂O > Cl⁻.

4 Option (1) is instantly recognized in 5 seconds!

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Why You Can 100% Trust This Shortcut: Spectrochemical series experimentally established via UV-vis crystal field splitting parameter Δ_o in octahedral complexes.

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Understand Crystal Field Splitting (Δ_o)

Crystal Field Theory (CFT) treats the interaction between metal d-orbitals and ligands as electrostatic and covalent π-interactions. Ligands that produce large splitting of the d-orbitals are called strong-field ligands, while those that produce small splitting are weak-field ligands.

\Delta_o(\text{strong field}) > \Delta_o(\text{weak field})

• Strong field: Low spin complexes (pairing occurs).
• Weak field: High spin complexes.

Step 2

Examine the Spectrochemical Series

The experimentally determined spectrochemical series arranges ligands in order of increasing field strength: I⁻ < Br⁻ < S²⁻ < SCN⁻ < Cl⁻ < N₃⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < edta⁴⁻ < NH₃ < en < CN⁻ < CO

\text{Cl}^- < \text{H}_2\text{O} < \text{NH}_3 < \text{CO}

• CO (Carbonyl): Strongest known ligand due to synergistic π-backbonding.
• NH₃: Nitrogen-donor ligand, stronger than oxygen-donors.
• H₂O: Oxygen-donor ligand, intermediate field strength.
• Cl⁻: Weak field halide donor due to repulsive π-donor interactions.

Step 3

Arrange in Decreasing Order of Strength

Inverting to decreasing order gives: CO > NH₃ > H₂O > Cl⁻

\text{CO} > \text{NH}_3 > \text{H}_2\text{O} > \text{Cl}^-

• Matches Option (1).

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 A

✓ 100% Correct

Verdict & Scientific Reason:

Perfect match with the standard IUPAC/NCERT spectrochemical series.

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Why this is airtight: None; canonical inorganic knowledge.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Places H₂O ahead of NH₃, but NH₃ (N-donor) has a higher field strength than H₂O (O-donor).

⚠️

Student Fallacy (Why candidates pick this trap): Swapping NH₃ and H₂O in the spectrochemical series.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Completely inverted order (increasing instead of decreasing).

⚠️

Student Fallacy (Why candidates pick this trap): Reading the question decreasing vs increasing prompt backwards.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Claims chloride is the strongest field ligand and CO is the weakest.

⚠️

Student Fallacy (Why candidates pick this trap): Gross misunderstanding of crystal field splitting.

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NTA Trap Alert: Confusing NH₃ and H₂O Placement

The most common point of confusion is whether NH₃ or H₂O is stronger. N-donors are less electronegative than O-donors and donate their lone pairs more readily, making NH₃ stronger than H₂O.

🛡️ How to avoid the -1 mark: Remember C > N > O > Halogen: Carbonyl > Ammine > Aqua > Halo.

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Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Coordination Compounds Standard Benchmark

Core Scientific Principle Tested:

"Ligand field strength increases from halide donors to oxygen, nitrogen, and carbon donors."

Syllabus Focus: Crystal Field Theory - Spectrochemical Series

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Can Not Overcome Chlorine: C (CO) > N (NH₃) > O (H₂O) > Cl (Cl⁻)!

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NEET 2026 Chemistry Question 58 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Donor Atom Hierarchy Rule: C > N > O > Halogen

Step-by-Step Rigorous Workflow & Mathematical Proof

Understand Crystal Field Splitting (Δ_o)

Examine the Spectrochemical Series

Arrange in Decreasing Order of Strength

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing NH₃ and H₂O Placement

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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