Q.82 Chemistry ⭐ 360° Option Elimination Active

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NEET 2023 Chemistry Question 82 Solution

Topic: Organic Chemistry – Some Basic Principles and Techniques · Official NTA Booklet Code G5

Question

The number of o bonds, 7 bonds and lone pair of electrons in pyridine, respectively are:

(1)12, 2,1
(2)11, 2, 0
(3)12, 3,0
(4)11, 3,1

✓

Verified Against NTA Final Answer Key

Option (4) : 11, 3, 1

📚 Organic Chemistry – Some Basic Principles and Techniques Medium

📋 Given Parameters & Problem Setup

Molecule Pyridine (C₅H₅N)

Quantities to determine Number of σ bonds, π bonds, and lone pairs of electrons

⚡

The 30-Second Exam Hall Shortcut: ⚡ Pyridine Skeletal Inventory: 11 σ, 3 π, and 1 Lone Pair

⏱️ Save ~30 seconds

Pyridine formula is C₅H₅N. Number of σ bonds = (Ring bonds) + (C–H bonds) = 6 + 5 = 11. Conjugated aromatic π bonds = 3 (aromatic sextet). Nitrogen has 1 unshared lone pair in an sp² hybrid orbital in the ring plane = 1 lone pair. Sequence: 11, 3, 1 in 10 seconds!

1 Total atoms: 5 carbons, 5 hydrogens, 1 nitrogen (11 atoms).

2 Ring framework σ bonds: 5 C–C/C=C + 1 C–N/C=N = 6 σ bonds in the ring.

3 Exocyclic σ bonds: 5 C–H single bonds.

4 Total σ bonds = 6 + 5 = 11.

5 Alternating double bonds in aromatic ring = 3 π bonds.

6 Nitrogen lone pair: occupies an sp² hybrid orbital in the ring plane = 1 lone pair.

7 Answer triplet: 11, 3, 1 (Option 4).

🛡️

Why You Can 100% Trust This Shortcut: Valence bond theory structure of heterocyclic pyridine C₅H₅N.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Determine the Molecular Structure of Pyridine

Pyridine has the chemical formula C₅H₅N. It consists of a planar hexagonal ring of 5 carbon atoms and 1 nitrogen atom, with each carbon bonded to one hydrogen atom:

\text{Pyridine: } \text{C}_5\text{H}_5\text{N} \quad (\text{Planar 6-membered aromatic ring})

Step 2

Count Sigma (σ) Bonds

Sum the ring skeletal bonds and the peripheral C–H single bonds:

\text{Ring } \sigma \text{ bonds} = 6, \quad \text{C–H } \sigma \text{ bonds} = 5 \implies \text{Total } \sigma \text{ bonds} = 6 + 5 = 11

Step 3

Count Pi (π) Bonds

The aromatic sextet consists of 6 delocalized π electrons distributed across 3 conjugated double bonds:

\text{Delocalized } 6\pi \text{ system} \implies \text{Total } \pi \text{ bonds} = 3

Step 4

Identify the Lone Pair on Nitrogen

The nitrogen atom in pyridine is sp² hybridized. One unhybridized p_z orbital contributes 1 electron to the aromatic π cloud, while the third sp² hybrid orbital holds an unshared lone pair in the ring plane:

\text{Nitrogen lone pair} = 1 \quad (\text{localized in an } sp^2 \text{ orbital, orthogonal to the } \pi \text{ system})

⭐

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:

Overcounts σ bonds (12 instead of 11) and undercounts π bonds (2 instead of 3).

⚠️

Student Fallacy (Why candidates pick this trap): Candidate miscounted the number of double bonds in the aromatic ring.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

Undercounts π bonds and claims zero lone pairs on nitrogen.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate incorrectly assumed nitrogen’s lone pair participates in the aromatic ring (like in pyrrole).

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Overcounts σ bonds and ignores the nitrogen lone pair.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate counted an extra σ bond on the nitrogen atom.

4 (4)

✓ 100% Correct

Verdict & Scientific Reason:

Accurate: 11 σ bonds (6 ring + 5 C-H), 3 π bonds (aromatic sextet), and 1 localized lone pair on nitrogen.

💡

Why this is airtight: None. Candidate correctly visualized all bonded pairs and non-bonding electrons.

⚠️

NTA Trap Alert: Confusing Pyridine with Pyrrole Aromaticity

In pyrrole, the nitrogen lone pair resides in a p-orbital and is part of the aromatic sextet (so it is delocalized and has no basic character). In pyridine, the aromatic sextet comes from the 5 carbon p-electrons and 1 nitrogen p-electron; nitrogen’s lone pair is localized in an sp² hybrid orbital in the ring plane and counts as 1 distinct lone pair!

🛡️ How to avoid the -1 mark: Remember: Pyridine = lone pair is sp² and NOT in the π-system. Total lone pairs = 1.

📖

Core NEET Syllabus Standard

National Eligibility cum Entrance Test (NEET UG) · Organic Chemistry – Some Basic Principles and Techniques Standard Benchmark

Core Scientific Principle Tested:

"Every single bond is a σ bond; double bonds contain one σ and one π bond; lone pairs occupy non-bonding hybrid or atomic orbitals."

Syllabus Focus: Structure and Hybridisation of Organic Compounds

Preserved in Rationalized Curriculum Syllabus & Academic Standards ↗

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NEET 2023 Chemistry Question 82 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Pyridine Skeletal Inventory: 11 σ, 3 π, and 1 Lone Pair

Step-by-Step Rigorous Workflow & Mathematical Proof

Determine the Molecular Structure of Pyridine

Count Sigma (σ) Bonds

Count Pi (π) Bonds

Identify the Lone Pair on Nitrogen

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Pyridine with Pyrrole Aromaticity

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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