Q.87 Chemistry ⭐ 360° Option Elimination Active

NEET 2025 Chemistry Question 87 Solution

Topic: Chemical Bonding and Molecular Structure · Official NTA Booklet Code 45

Question

Identify the correct orders against the property mentioned A. H₂O > NH₃ > CHCl₃ – dipole moment B. XeF₄ > XeO₃ > XeF₂ – number of lone pairs on central atom C. O–H > C–H > N–O – bond length D. N₂ > O₂ > H₂ – bond enthalpy Choose the correct answer from the options given below:

✓

Verified Against NTA Final Answer Key

Option (1) : A, D only

📚 Chemical Bonding and Molecular Structure Medium

📋 Given Parameters & Problem Setup

Order A (Dipole Moment) H₂O > NH₃ > CHCl₃

Order B (Lone Pairs on Xe) XeF₄ > XeO₃ > XeF₂

Order C (Bond Length) O-H > C-H > N-O

Order D (Bond Enthalpy) N₂ > O₂ > H₂

⚡

The 30-Second Exam Hall Shortcut: ⚡ Canonical Data Cross-Verification

⏱️ Save ~40 seconds

A: Dipole moments: H₂O (1.85 D) > NH₃ (1.47 D) > CHCl₃ (1.04 D) ⟹ TRUE! B: Lone pairs: XeF₂ (3) > XeF₄ (2) > XeO₃ (1), so B is FALSE! C: O-H (96 pm) is SHORTEST, not longest ⟹ FALSE! D: N₂ (946 kJ/mol, triple bond) > O₂ (498, double) > H₂ (436, single) ⟹ TRUE! ⟹ A, D only!

1 Check Order A (Dipole moment): H₂O has μ = 1.85 D; NH₃ has μ = 1.47 D; CHCl₃ has μ = 1.04 D. The order H₂O > NH₃ > CHCl₃ is TRUE.

2 Check Order B (Lone pairs on Xe): Xe has 8 valence electrons. XeF₄ has (8-4)/2 = 2 lone pairs; XeO₃ has (8-6)/2 = 1 lone pair; XeF₂ has (8-2)/2 = 3 lone pairs. The statement claims 2 > 1 > 3, which is mathematically and chemically FALSE.

3 Check Order C (Bond length): O-H bond length is ~96 pm; C-H is ~109 pm; N-O single bond is ~140 pm. The true order is N-O > C-H > O-H. Order C claims O-H is longest ⟹ FALSE.

4 Check Order D (Bond dissociation enthalpy): N₂ has a strong triple bond (946 kJ/mol); O₂ has a double bond (498 kJ/mol); H₂ has a single bond (436 kJ/mol). The order N₂ > O₂ > H₂ is TRUE.

5 Conclusion: Orders A and D only are correct.

6 Select Option (1) in under 15 seconds!

🛡️

Why You Can 100% Trust This Shortcut: Half-Life and Arrhenius Activation Energy (NCERT Chemistry · Chemical Kinetics: t_1/2 = 0.693/k).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Evaluate Order A (Dipole Moments of H₂O, NH₃, and CHCl₃)

Examine experimental dipole moment values in Debye (D) from NCERT Chapter 4:

\mu(\text{H}_2\text{O}) = 1.85\text{ D} > \mu(\text{NH}_3) = 1.47\text{ D} > \mu(\text{CHCl}_3) = 1.04\text{ D}

• H₂O has two bond dipoles adding vectorially to two lone pairs in a bent geometry.
• NH₃ has three bond dipoles reinforcing the single lone pair in a pyramidal geometry.
• CHCl₃ has opposing C-H and C-Cl bond dipoles, resulting in a net moment of 1.04 D.
• Order A is completely TRUE.

Step 2

Evaluate Orders B and C (Lone Pairs on Xenon & Bond Lengths)

Determine the number of non-bonding electron pairs on xenon and compare covalent radii:

\text{Lone pairs on Xe: } \text{XeF}_2\,(3) > \text{XeF}_4\,(2) > \text{XeO}_3\,(1)

• Order B claims XeF₄ > XeO₃ > XeF₂, which contradicts the true count. Order B is FALSE.
• Covalent bond lengths: N-O single bond (140 pm) > C-H bond (109 pm) > O-H bond (96 pm).
• Order C claims O-H > C-H > N-O, which is the exact reverse. Order C is FALSE.

Step 3

Evaluate Order D (Bond Dissociation Enthalpies of Diatomic Molecules)

Compare bond dissociation enthalpies from NCERT thermodynamics and chemical bonding data:

\Delta_{bond} H^\circ: \; \text{N}_2\,(945.8\text{ kJ/mol}) > \text{O}_2\,(498.3\text{ kJ/mol}) > \text{H}_2\,(435.8\text{ kJ/mol})

• N₂ possesses a triple bond (:N≡N:), O₂ possesses a double bond (O=O), and H₂ has a single bond (H-H).
• The order N₂ > O₂ > H₂ is completely TRUE.
• Therefore, A and D only are correct, matching Option (1).

⭐

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:

100% correct. Both dipole moment hierarchy (A) and bond enthalpy order (D) are factually exact.

💡

Why this is airtight: None; precise recall of NCERT tables.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Order B is false (XeF₂ has 3 lone pairs, more than XeF₄ and XeO₃).

⚠️

Student Fallacy (Why candidates pick this trap): Miscounting lone pairs on XeF₂.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Order C is false (O-H is ~96 pm, much shorter than N-O ~140 pm).

⚠️

Student Fallacy (Why candidates pick this trap): Believing O-H is the longest bond.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Both B and C are false.

⚠️

Student Fallacy (Why candidates pick this trap): Selecting two invalid statements.

⚠️

NTA Trap Alert: Assuming H₂ Has a Stronger Bond Than O₂

Students often know H₂ has a very strong single bond (436 kJ/mol) and forget that O₂ has a DOUBLE bond (498 kJ/mol)! The double bond of O₂ requires more energy to break than the single bond of H₂, making N₂ (946) > O₂ (498) > H₂ (436) completely true!

🛡️ How to avoid the -1 mark: Bond order check: N₂ (B.O. = 3, ~946) > O₂ (B.O. = 2, ~498) > H₂ (B.O. = 1, ~436).

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Chemical Bonding and Molecular Structure Standard Benchmark

Core Scientific Principle Tested:

"H₂O > NH₃ > CHCl₃ (dipole); N₂ > O₂ > H₂ (bond enthalpy)."

Syllabus Focus: Dipole Moments & Bond Enthalpies of Diatomic Molecules

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Dipole: H₂O > NH₃ > CHCl₃ (A). Bond: Triple (N₂) > Double (O₂) > Single (H₂) (D) ⟹ A & D only!

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NEET 2025 Chemistry Question 87 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Canonical Data Cross-Verification

Step-by-Step Rigorous Workflow & Mathematical Proof

Evaluate Order A (Dipole Moments of H₂O, NH₃, and CHCl₃)

Evaluate Orders B and C (Lone Pairs on Xenon & Bond Lengths)

Evaluate Order D (Bond Dissociation Enthalpies of Diatomic Molecules)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Assuming H₂ Has a Stronger Bond Than O₂

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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