Q.60 Chemistry ⭐ 360° Option Elimination Active

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NEET 2025 Chemistry Question 60 Solution

Topic: Hydrocarbons & Amines · Official NTA Booklet Code 45

Question

Which one of the following reactions does NOT give benzene as the product??;

✓

Verified Against NTA Final Answer Key

Option (4) : Benzenediazonium chloride + H₂O / warm (Yields Phenol, NOT Benzene)

📚 Hydrocarbons & Amines Easy

📋 Given Parameters & Problem Setup

Reaction (1) Sodium benzoate + sodalime / Δ (Decarboxylation)

Reaction (2) n-Hexane + Mo₂O₃ / 773 K, 10-20 atm (Aromatization)

Reaction (3) Ethyne (HC≡CH) + red hot Iron tube at 873 K (Cyclic polymerization)

Reaction (4) Benzenediazonium chloride (Ph-N₂⁺Cl⁻) + H₂O / warm

⚡

The 30-Second Exam Hall Shortcut: ⚡ Diazonium Hydrolysis Phenol Trap

⏱️ Save ~30 seconds

Ph-N₂⁺Cl⁻ + H₂O (warm) produces PHENOL (Ph-OH), NOT benzene! (To get benzene, you need H₃PO₂ or ethanol)! Reactions (1), (2), and (3) are classic textbook preparations of benzene! ⟹ Reaction (4) does NOT give benzene!

1 Reaction (1): Decarboxylation of sodium benzoate using sodalime (NaOH + CaO) removes CO₂ to give BENZENE.

2 Reaction (2): Aromatization / catalytic reforming of n-hexane over Mo₂O₃ / Al₂O₃ at 773 K gives BENZENE.

3 Reaction (3): Cyclic trimerization of acetylene (ethyne) passed through red hot iron tube gives BENZENE.

4 Reaction (4): Warming benzenediazonium chloride with plain water hydrolyzes the diazonium group into a phenolic -OH group, forming PHENOL (C₆H₅OH) + N₂ + HCl!

5 Therefore, Reaction (4) does NOT give benzene!

6 Select Option (4) in under 10 seconds!

🛡️

Why You Can 100% Trust This Shortcut: Electrophilic Aromatic Substitution & Sandmeyer Reactions (NCERT Chemistry · Hydrocarbons & Amines).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Evaluate Benzene Preparations in Reactions (1), (2), and (3)

Verify the products of the first three reactions from standard NCERT organic chemistry:

(1) \; \text{C}_6\text{H}_5\text{COONa} + \text{NaOH} \xrightarrow{\text{CaO}, \Delta} \text{C}_6\text{H}_6 + \text{Na}_2\text{CO}_3 \quad (\text{Benzene})

• (2) n-Hexane (CH₃(CH₂)₄CH₃) undergoes aromatization over Mo₂O₃/Al₂O₃ at 773 K and 10–20 atm to yield Benzene + 4 H₂.
• (3) 3 HC≡CH undergoes cyclic trimerization in a red hot iron tube at 873 K to yield Benzene.

Step 2

Analyze Hydrolysis of Benzenediazonium Chloride (Reaction 4)

When benzenediazonium chloride solution is warmed with water, nucleophilic substitution by H₂O takes place with evolution of nitrogen gas:

\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{H}_2\text{O} \xrightarrow{\text{warm}} \text{C}_6\text{H}_5\text{OH} \text{ (Phenol)} + \text{N}_2 \uparrow + \text{HCl}

• The organic product is PHENOL, not benzene.
• To reduce benzenediazonium chloride to benzene, hypophosphorous acid (H₃PO₂ + H₂O) or ethanol (CH₃CH₂OH) must be used.

Step 3

Conclusion and Match

Since Reaction (4) produces phenol and does NOT give benzene, it is the correct answer to the question.

\text{Reaction that does NOT yield benzene: Reaction (4)}

• Matches Option (4) with 100% precision.

⭐

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

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Decarboxylation yields benzene.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking decarboxylation gives benzoic acid.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Catalytic aromatization yields benzene.

⚠️

Student Fallacy (Why candidates pick this trap): Unfamiliar with catalytic reforming of alkanes.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Trimerization of ethyne is the classic Berthelot synthesis of benzene.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking ethyne polymerizes into polyacetylene instead of benzene.

4 D

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. This reaction yields PHENOL (C₆H₅OH), not benzene.

💡

Why this is airtight: None; flawless recall of diazonium chemistry.

⚠️

NTA Trap Alert: Confusing Diazonium Reduction (H₃PO₂) with Hydrolysis (H₂O)

Students often confuse the reagents for diazonium salts. Heating with H₃PO₂ or ethanol replaces -N₂⁺Cl⁻ with -H to give BENZENE. Heating with plain water replaces it with -OH to give PHENOL!

🛡️ How to avoid the -1 mark: Remember: Water gives PHENOL; Hypophosphorous acid gives BENZENE!

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Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Amines Standard Benchmark

Core Scientific Principle Tested:

"Hydrolysis of benzenediazonium chloride with warm water yields phenol (Ph-OH)."

Syllabus Focus: Reactions of Diazonium Salts

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Diazonium + Warm Water = PHENOL! (Needs H₃PO₂ for Benzene) ⟹ Reaction (4)!

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NEET 2025 Chemistry Question 60 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Diazonium Hydrolysis Phenol Trap

Step-by-Step Rigorous Workflow & Mathematical Proof

Evaluate Benzene Preparations in Reactions (1), (2), and (3)

Analyze Hydrolysis of Benzenediazonium Chloride (Reaction 4)

Conclusion and Match

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Diazonium Reduction (H₃PO₂) with Hydrolysis (H₂O)

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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