Q.46 Chemistry ⭐ 360° Option Elimination Active

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NEET 2026 Chemistry Question 46 Solution

Topic: Aldehydes, Ketones and Carboxylic Acids & Haloalkanes · Official NTA Booklet Code 50

Question

For the following reaction sequence, choose the correct option: Benzene → i. CH₃COCl, AlCl₃ ii. NaOCl → P + Q

✓

Verified Against NTA Final Answer Key

Option (3) : If P gives a carboxylic acid on acidification, Q gives a poisonous gas on exposure to air and light.

📚 Aldehydes, Ketones and Carboxylic Acids & Haloalkanes Medium

📋 Given Parameters & Problem Setup

Starting Material Benzene (C₆H₆)

Reagent (i) CH₃COCl + Anhydrous AlCl₃ (Friedel-Crafts Acylation)

Reagent (ii) NaOCl (Sodium Hypochlorite / Haloform reagent)

Products P (carboxylate salt) + Q (haloform)

⚡

The 30-Second Exam Hall Shortcut: ⚡ The Methyl Ketone + Hypochlorite Fingerprint

⏱️ Save ~95 seconds

Spot the tandem: Benzene + Acetyl Chloride = Acetophenone (a methyl ketone). NaOCl is the textbook Haloform reagent!

1 Identify Intermediate: Benzene + CH₃COCl/AlCl₃ → Acetophenone (Ph-CO-CH₃).

2 Recognize Haloform Reagent: NaOCl = Cl₂ + NaOH. It cleaves the methyl ketone group into Sodium Benzoate (P) and Chloroform (Q = CHCl₃).

3 Direct Link to Statement 3: Chloroform (CHCl₃) when exposed to air and sunlight oxidizes into deadly Phosgene gas (COCl₂)! P upon acidification gives Benzoic Acid.

4 Zero doubt: Pick Option (3) immediately in 15 seconds!

🛡️

Why You Can 100% Trust This Shortcut: In standard organic chemistry, NaOCl is the definitive chlorinating oxidizer for haloform cleavage. The conversion of chloroform into poisonous phosgene (COCl₂) under sunlight is an established canonical reaction.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Electrophilic Aromatic Substitution: Friedel-Crafts Acylation

Benzene reacts with acetyl chloride in the presence of anhydrous aluminium chloride (Lewis acid catalyst). An acylium ion (CH₃-C⁺=O) is generated, which attacks the benzene ring to yield acetophenone.

\text{C}_6\text{H}_6 + \text{CH}_3\text{COCl} \xrightarrow{\text{anh. AlCl}_3} \text{C}_6\text{H}_5\text{COCH}_3 + \text{HCl}

• Electrophile: CH₃-C⁺=O (resonance-stabilized acylium cation).
• Product: Acetophenone (methyl phenyl ketone).

Step 2

Haloform Reaction with Sodium Hypochlorite (NaOCl)

Acetophenone contains the characteristic -COCH₃ group attached to carbon. Sodium hypochlorite (NaOCl), an aqueous mixture of chlorine and sodium hydroxide, oxidizes and halogenates the methyl ketone. Tri-alpha chlorination occurs followed by hydroxide attack and cleavage of the C-C bond to yield Sodium Benzoate (P) and Chloroform (Q).

\text{C}_6\text{H}_5\text{COCH}_3 + 3\text{NaOCl} \to \text{C}_6\text{H}_5\text{COONa} (P) + \text{CHCl}_3 (Q) + 2\text{NaOH}

• Product P: Sodium benzoate (C₆H₅COONa).
• Product Q: Chloroform / trichloromethane (CHCl₃).

Step 3

Chemical Properties of P and Q (Acidification & Atmospheric Oxidation)

Acidification of sodium benzoate (P) yields Benzoic Acid (C₆H₅COOH). When chloroform (Q) is exposed to atmospheric oxygen in the presence of sunlight, it undergoes slow photochemical oxidation to form carbonyl chloride (Phosgene, COCl₂), an extremely poisonous gas.

2\text{CHCl}_3 + \text{O}_2 \xrightarrow{\text{light}} 2\text{COCl}_2\text{ (Phosgene, poisonous)} + 2\text{HCl}

• Acidification: C₆H₅COONa + H⁺ → C₆H₅COOH (Benzoic acid).
• Safety protocol in labs: Chloroform is stored in dark amber bottles filled to the brim with 1% ethanol added as a stabilizer.

⭐

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:

Completely false. P is sodium benzoate (C₇H₅O₂Na) and Q is chloroform (CHCl₃); their molecular weights and atom compositions are entirely different.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing functional group cleavage with a rearrangement reaction.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Neither an alcohol nor an ether is generated in haloform cleavage of a methyl ketone.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming reduction or substitution rather than haloform cleavage.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Scientifically rigorous. P = Sodium benzoate (acidifies to Benzoic Acid) and Q = Chloroform (oxidizes to poisonous Phosgene gas COCl₂).

💡

Why this is airtight: None; matches the textbook oxidation mechanism of chloroform.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Chloroform (CHCl₃) with base undergoes alpha-elimination to generate dichlorocarbene (:CCl₂), or hydrolyzes to sodium formate (HCOONa), not an alkene.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking of dehydrohalogenation of an alkyl halide to form an alkene (which requires at least 2 carbon atoms).

⚠️

NTA Trap Alert: Forgetting the Storage Danger of Chloroform

Students frequently remember the haloform mechanism but forget the industrial toxicology of chloroform (photochemical oxidation to phosgene COCl₂).

🛡️ How to avoid the -1 mark: Always remember: Chloroform (CHCl₃) + sunlight + air = deadly Phosgene (COCl₂). That is why 1% ethanol is added to commercial chloroform.

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Aldehydes, Ketones & Haloalkanes Standard Benchmark

Core Scientific Principle Tested:

"Methyl ketones undergo hypohalite cleavage to yield carboxylate salts and trihalomethanes. Chloroform photochemically oxidizes to phosgene."

Syllabus Focus: Haloform reaction and oxidation of polyhalogen compounds

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Methyl ketone + Hypochlorite = Benzoate (P) + Chloroform (Q). Chloroform + Sun = Phosgene poison!

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NEET 2026 Chemistry Question 46 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ The Methyl Ketone + Hypochlorite Fingerprint

Step-by-Step Rigorous Workflow & Mathematical Proof

Electrophilic Aromatic Substitution: Friedel-Crafts Acylation

Haloform Reaction with Sodium Hypochlorite (NaOCl)

Chemical Properties of P and Q (Acidification & Atmospheric Oxidation)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Forgetting the Storage Danger of Chloroform

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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