Q.86 Chemistry ⭐ 360° Option Elimination Active

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NEET 2026 Chemistry Question 86 Solution

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

Question

Consider the following reaction, and choose the correct option. Toluene → i. CrO₂Cl₂, CS₂ ii. H₃O⁺ → P

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Verified Against NTA Final Answer Key

Option (4) : Compound P is obtained by the hydrogenation of benzoyl chloride with Pd on BaSO₄.

📚 Aldehydes, Ketones and Carboxylic Acids Medium

📋 Given Parameters & Problem Setup

Reaction Toluene + (i. CrO₂Cl₂, CS₂; ii. H₃O⁺) → Compound P

Reactant Toluene (methylbenzene)

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The 30-Second Exam Hall Shortcut: ⚡ The Étard Reaction Identifier

⏱️ Save ~70 seconds

Toluene + Chromyl Chloride (CrO₂Cl₂) = Étard Reaction producing BENZALDEHYDE (P)!

1 Identify named reaction: Oxidation of methylbenzene with CrO₂Cl₂ in CS₂ followed by hydrolysis is the textbook ÉTARD REACTION.

2 The product P is unequivocally BENZALDEHYDE (Ph-CHO)!

3 Scan Options for Benzaldehyde reactions:

4 Option (1): Gives brisk effervescence with NaHCO₃? FALSE (that requires carboxylic acid, -COOH).

5 Option (2): Benzene + CH₃COCl/AlCl₃? FALSE (that gives Acetophenone, Ph-CO-CH₃).

6 Option (3): White precipitate with bromine water? FALSE (that is Phenol / Aniline).

7 Option (4): Hydrogenation of benzoyl chloride with Pd on BaSO₄ (Rosenmund Reduction)? TRUE! Ph-COCl + H₂ → Ph-CHO!

8 Option (4) is undeniably correct in 15 seconds!

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Why You Can 100% Trust This Shortcut: Both the Étard reaction and Rosenmund reduction are premier canonical named reactions for the preparation of aromatic aldehydes in NCERT Chemistry.

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Identify Compound P via the Étard Reaction

Chromyl chloride (CrO₂Cl₂) in a non-polar solvent like CS₂ oxidizes the methyl group of toluene into a brown chromium complex [C₆H₅CH(OCrOHCl₂)₂]. Hydrolysis of this intermediate yields benzaldehyde.

\text{C}_6\text{H}_5\text{CH}_3 \xrightarrow[\text{ii. } \text{H}_3\text{O}^+]{\text{i. } \text{CrO}_2\text{Cl}_2, \text{ CS}_2} \text{C}_6\text{H}_5\text{CHO} \;(\mathbf{P} = \text{Benzaldehyde})

• Compound P is Benzaldehyde (C₆H₅CHO).

Step 2

Evaluate Statement (4): Rosenmund Reduction

Rosenmund reduction involves catalytic hydrogenation of an acyl chloride (benzoyl chloride) over palladium catalyst supported on barium sulfate (Pd/BaSO₄), partially poisoned with sulfur or quinoline to prevent over-reduction to an alcohol.

\text{C}_6\text{H}_5\text{COCl} + \text{H}_2 \xrightarrow{\text{Pd/BaSO}_4} \text{C}_6\text{H}_5\text{CHO} \;(\mathbf{P}) + \text{HCl}

• This independently synthesizes Compound P (Benzaldehyde).
• Statement (4) is scientifically correct.

Step 3

Demonstrate Invalidation of Statements (1), (2), and (3)

1. Statement (1): Benzaldehyde is an aldehyde, not a carboxylic acid; it does NOT release CO₂ gas with NaHCO₃ (no brisk effervescence). 2. Statement (2): Benzene + CH₃COCl/AlCl₃ is Friedel-Crafts acylation, producing Acetophenone (PhCOCH₃), not benzaldehyde. 3. Statement (3): Bromine water gives white precipitates with phenol (2,4,6-tribromophenol) or aniline, not benzaldehyde.

\text{Option (4) is the only true statement}

• Matches Option (4).

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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

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Benzaldehyde is not acidic enough to decompose bicarbonate to CO₂.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing benzaldehyde with benzoic acid.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Friedel-Crafts acylation of benzene with acetyl chloride yields acetophenone, not benzaldehyde.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing benzaldehyde with acetophenone.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. White precipitate with bromine water is a test for phenol or aniline, not benzaldehyde.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing benzaldehyde with phenol.

4 D

✓ 100% Correct

Verdict & Scientific Reason:

Exact match: Rosenmund reduction of benzoyl chloride over Pd/BaSO₄ gives benzaldehyde (Compound P).

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Why this is airtight: None; flawless cross-connection of named synthetic pathways.

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NTA Trap Alert: Thinking Toluene Oxidation Gives Benzoic Acid Directly

Vigorous oxidizers like alkaline KMnO₄ oxidize toluene to benzoic acid. But CrO₂Cl₂ (Étard reaction) is specifically designed to STOP at the aldehyde stage (Benzaldehyde)!

🛡️ How to avoid the -1 mark: CrO₂Cl₂ stops at Benzaldehyde; KMnO₄ goes all the way to Benzoic Acid.

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Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Aldehydes, Ketones and Carboxylic Acids Standard Benchmark

Core Scientific Principle Tested:

"Toluene + CrO₂Cl₂ yields benzaldehyde; Benzoyl chloride + H₂/Pd-BaSO₄ also yields benzaldehyde."

Syllabus Focus: Preparation of aromatic aldehydes - Étard reaction and Rosenmund reduction

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Étard stops at Benzaldehyde; Rosenmund reduces acid chloride to the same aldehyde!

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NEET 2026 Chemistry Question 86 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ The Étard Reaction Identifier

Step-by-Step Rigorous Workflow & Mathematical Proof

Identify Compound P via the Étard Reaction

Evaluate Statement (4): Rosenmund Reduction

Demonstrate Invalidation of Statements (1), (2), and (3)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Thinking Toluene Oxidation Gives Benzoic Acid Directly

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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