Q.97 Chemistry · Section B ⭐ 360° Option Elimination Active

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NEET 2024 Chemistry Question 97 Solution

Topic: Chemical Bonding and Molecular Structure · Official NTA Booklet Code T1

Question

— Identify the correct answer.

✓

Verified Against NTA Final Answer Key

Option (2) : Three canonical forms can be drawn for CO3²⁻ ion.

📚 Chemical Bonding and Molecular Structure Easy

📋 Given Parameters & Problem Setup

Option 1 statement Dipole moment of NF3 is greater than that of NH3

Option 2 statement Three canonical forms can be drawn for CO3²⁻ ion

Option 3 statement Three resonance structures can be drawn for ozone

Option 4 statement BF3 has non-zero dipole moment

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The 30-Second Exam Hall Shortcut: ⚡ Carbonate Resonance Canonical Form Rule

⏱️ Save ~35 seconds

Carbonate CO3²⁻ has 3 equivalent oxygen atoms sharing one double bond and two single bonds -> Exactly THREE canonical Lewis forms! Option (2) is TRUE!

1 Check Option (1): In NH3, N-H bond dipoles add to the lone pair dipole (μ = 1.47 D). In NF3, electronegative fluorines pull in the opposite direction to the lone pair, opposing it (μ = 0.24 D). Thus, μ(NH3) > μ(NF3) -> Option (1) is FALSE.

2 Check Option (2): In carbonate ion CO3²⁻, the central carbon is bonded to three oxygens. The C=O double bond can reside with oxygen 1, oxygen 2, or oxygen 3. Exactly 3 equivalent canonical forms -> Option (2) is TRUE!

3 Check Option (3): Ozone (O3) has only 2 main canonical resonance Lewis structures (O=O⁺-O⁻ ↔ ⁻O-O⁺=O) -> Option (3) is FALSE.

4 Check Option (4): BF3 has symmetrical trigonal planar geometry (120° bond angles); the three B-F bond dipoles cancel to yield μ = 0 (zero dipole moment) -> Option (4) is FALSE.

5 Option (2) in 5 seconds!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · Chemical Bonding and Molecular Structure (Resonance structures of CO3 2-, ozone, and dipole moments of NH3 vs NF3 and BF3).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Analysis of Carbonate Resonance Structures (Statement 2)

In the carbonate ion (CO3²⁻), the carbon atom forms one double bond (C=O) and two single bonds (C-O⁻) with formal charges -1 on each single-bonded oxygen. Because all three oxygens are chemically and spatially equivalent, the double bond is delocalized equally among the three oxygen atoms, generating three equivalent canonical Lewis resonance structures:

[:\ddot{\text{O}}=\text{C}(\ddot{\text{O}}:^\ominus)_2] \longleftrightarrow [^\ominus:\ddot{\text{O}}{-}\text{C}(=\ddot{\text{O}}){-}\ddot{\text{O}}:^\ominus] \longleftrightarrow [(^\ominus:\ddot{\text{O}}{-})_2\text{C}=\ddot{\text{O}}:] \quad (\text{3 canonical forms})

Step 2

Analysis of NH3 versus NF3 Dipole Moments (Statement 1)

Both NH3 and NF3 have trigonal pyramidal geometries with one lone pair. In NH3, nitrogen is more electronegative than hydrogen, so N-H bond dipoles reinforce the lone pair dipole: μ = 1.47 D. In NF3, fluorine is more electronegative than nitrogen, so N-F bond dipoles oppose the lone pair dipole, resulting in a tiny net dipole: μ = 0.24 D. Hence μ(NH3) > μ(NF3). Statement 1 is false.

\mu(\text{NH}_3) = 1.47\;\text{D} \;>\; \mu(\text{NF}_3) = 0.24\;\text{D}

Step 3

Analysis of Ozone Resonance (Statement 3)

Ozone (O3) is an angular molecule with a central oxygen atom bonded to two terminal oxygens. It possesses only TWO principal canonical resonance structures:

\ddot{\text{O}}=\overset{\oplus}{\ddot{\text{O}}}{-}\ddot{\text{O}}:^\ominus \longleftrightarrow \,:^\ominus\ddot{\text{O}}{-}\overset{\oplus}{\ddot{\text{O}}}=\ddot{\text{O}} \quad (\text{2 resonance structures, not 3})

Step 4

Analysis of BF3 Dipole Moment (Statement 4)

Boron trifluoride (BF3) has sp² hybridization and symmetrical trigonal planar geometry with 120° bond angles. The vector sum of the three identical B-F bond dipole moments is identically zero:

\vec{\mu}_{net} = \vec{\mu}_1 + \vec{\mu}_2 + \vec{\mu}_3 = 0 \implies \text{Dipole moment of BF}_3 \text{ is ZERO}

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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 (1)

✗ Incorrect

Verdict & Scientific Reason:

False: μ(NH3) = 1.47 D > μ(NF3) = 0.24 D.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming higher electronegativity difference in N-F automatically gives higher dipole moment.

2 (2)

✓ 100% Correct

Verdict & Scientific Reason:

True: Carbonate has exactly 3 equivalent canonical Lewis resonance structures.

💡

Why this is airtight: None.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

False: Ozone has only 2 principal canonical forms.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing 3 oxygen atoms with 3 resonance structures.

4 (4)

✗ Incorrect

Verdict & Scientific Reason:

False: Trigonal planar symmetry cancels all bond dipoles to zero.

⚠️

Student Fallacy (Why candidates pick this trap): Forgetting vector cancellation in symmetric planar molecules.

⚠️

NTA Trap Alert: The NF3 vs NH3 Dipole Direction Trap

Even though fluorine is much more electronegative than hydrogen, in NF3 the bond dipoles oppose the lone pair, canceling most of the dipole. In NH3, they add constructively!

🛡️ How to avoid the -1 mark: Draw the dipole vectors: In NH3 arrows point up (constructive); in NF3 bond arrows point down (destructive).

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Core NEET Syllabus Standard

Chemistry Core Inorganic/Physical · Chemical Bonding and Molecular Structure Standard Benchmark

Core Scientific Principle Tested:

"Carbonate ion CO3 2- exhibits resonance among three equivalent canonical structures where the double bond is shared across each C-O bond."

Syllabus Focus: Resonance and Dipole Moments: Carbonate, Ozone, and NH3/NF3

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Three oxygens in carbonate take turns with the pi: Three canonical forms catch the eye!

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NEET 2024 Chemistry Question 97 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Carbonate Resonance Canonical Form Rule

Step-by-Step Rigorous Workflow & Mathematical Proof

Analysis of Carbonate Resonance Structures (Statement 2)

Analysis of NH3 versus NF3 Dipole Moments (Statement 1)

Analysis of Ozone Resonance (Statement 3)

Analysis of BF3 Dipole Moment (Statement 4)

360° Option Elimination Engine Key Feature

NTA Trap Alert: The NF3 vs NH3 Dipole Direction Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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