NEET Amines & Haloalkanes and Haloarenes PYQs with Solutions

NEET 2025 · Q74 Easy Preparation and Stability of Benzenediazonium Salts & Synthesis of Iodobenzene

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Official NEET 2025 Question 74 - Amines & Haloalkanes and Haloarenes

1 Both Statement I and Statement II are correct ✓ Key

2 Both Statement I and Statement II are incorrect

3 Statement I is correct but Statement II is incorrect

4 Statement I is incorrect but Statement II is correct

💡 Verified Solution & 30-Second Hack

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Verified Against NTA Final Answer Key

Option (1) : Both Statement I and Statement II are correct

📚 Amines & Haloalkanes and Haloarenes Easy

📋 Given Parameters & Problem Setup

Statement I Benzenediazonium salt is prepared by the reaction of aniline with nitrous acid at 273 - 278 K. It decomposes easily in the dry state.

Statement II Insertion of iodine into the benzene ring is difficult and hence iodobenzene is prepared through the reaction of benzenediazonium salt with KI.

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The 30-Second Exam Hall Shortcut: ⚡ NCERT Diazonium Verbatim Match

⏱️ Save ~30 seconds

Statement I: Diazotization is carried out at 0-5°C (273-278 K), and dry diazonium salt is notoriously explosive/decomposes easily (NCERT verbatim, TRUE)! Statement II: Direct iodination is reversible; reaction of ArN₂⁺Cl⁻ with KI is the standard synthesis of iodobenzene (NCERT verbatim, TRUE)! Both statements are CORRECT!

1 Examine Statement I: Diazotization of primary aromatic amines is conducted in ice-cold conditions (273–278 K). In the solid/dry state, benzenediazonium salts are thermally unstable and decompose explosively. NCERT text verbatim: "It decomposes easily in the dry state." Statement I is TRUE.

2 Examine Statement II: Direct electrophilic iodination of benzene is reversible due to generation of reducing agent HI (requires oxidants like HNO₃/HIO₄). Therefore, direct insertion of iodine is difficult. Treatment of benzenediazonium chloride with aqueous KI provides an efficient, non-catalytic route to iodobenzene: Ar-N₂⁺Cl⁻ + KI → Ar-I + KCl + N₂. Statement II is TRUE.

3 Conclusion: Both Statement I and Statement II are correct.

4 Select Option (1) in under 10 seconds!

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Why You Can 100% Trust This Shortcut: Arenediazonium Salts Stability and Displacement Reactions (NCERT Chemistry · Amines & Haloarenes).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Evaluate Statement I (Diazotization Conditions and Physical State)

Analyze the preparation and handling of benzenediazonium chloride from NCERT Amines:

\text{C}_6\text{H}_5\text{NH}_2 + \text{NaNO}_2 + 2\text{HCl} \xrightarrow{273-278\text{ K}} \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{NaCl} + 2\text{H}_2\text{O}

• Because diazonium salts are unstable at higher temperatures, the reaction must be kept at 0–5 °C (273–278 K).
• In aqueous solution at low temperature it is reasonably stable, but in the dry state it decomposes easily and explosively.
• Statement I is completely TRUE.

Step 2

Evaluate Statement II (Preparation of Iodobenzene via Diazonium Salt)

Analyze the synthetic route for iodobenzene from NCERT Haloalkanes and Haloarenes:

\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{KI} \longrightarrow \text{C}_6\text{H}_5\text{I} + \text{KCl} + \text{N}_2 \uparrow

• Direct halogenation with iodine (I₂) is reversible and very slow, yielding poor results unless an oxidizing acid is added to consume HI.
• Consequently, the diazonium reaction with potassium iodide (KI) without any catalyst is the preferred canonical method for synthesizing iodobenzene.
• Statement II is completely TRUE.

Step 3

Select Matching Option

Both Statement I and Statement II are correct:

\text{Statement I: Correct}, \quad \text{Statement II: Correct} \implies \text{Option (1)}

• Matches Option (1) with 100% precision.

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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:

100% correct. Both statements reflect established NCERT principles on diazonium salts.

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

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Both statements are factually sound.

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Student Fallacy (Why candidates pick this trap): Believing dry diazonium salts are stable.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Statement II is correct (KI is the standard method to introduce iodine).

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Student Fallacy (Why candidates pick this trap): Thinking direct iodination is facile.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Statement I is correct.

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Student Fallacy (Why candidates pick this trap): Doubting 273-278 K temperature range.

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NTA Trap Alert: Need for Cu Catalyst in Iodination

Candidates sometimes think Sandmeyer’s reaction requires Cu₂Cl₂ or Cu₂Br₂ for iodination too. For iodobenzene, NO copper catalyst is needed; simply warming with aqueous KI gives iodobenzene quantitatively!

🛡️ How to avoid the -1 mark: Remember: Sandmeyer uses Cu for Cl/Br, but KI alone is enough for Iodine!

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Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Amines Standard Benchmark

Core Scientific Principle Tested:

"Diazotization occurs at 273-278 K; dry salt decomposes; KI readily yields iodobenzene."

Syllabus Focus: Diazonium Salts: Preparation, Stability and Replacement by Iodine

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Ice cold to make, explosive when dry, and simply add KI for Iodobenzene ⟹ Both statements TRUE!

NEET Amines & Haloalkanes and Haloarenes Previous Year Questions with Solutions

The 30-Second Exam Hall Shortcut: ⚡ NCERT Diazonium Verbatim Match

Step-by-Step Rigorous Workflow & Mathematical Proof

Evaluate Statement I (Diazotization Conditions and Physical State)

Evaluate Statement II (Preparation of Iodobenzene via Diazonium Salt)

Select Matching Option

360° Option Elimination Engine Key Feature

NTA Trap Alert: Need for Cu Catalyst in Iodination

Core NEET Syllabus Standard

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