Q.71 Chemistry ⭐ 360° Option Elimination Active

NEET 2026 Chemistry Question 71 Solution

Topic: Solutions · Official NTA Booklet Code 50

Question

Consider the following statements about the solutions formed by mixing two liquids. A. An ideal solution thus formed obeys Raoult's law throughout the composition range. B. Mixture of chloroform and acetone shows negative deviation from Raoult's law. C. Mixture of aniline and phenol shows positive deviation from Raoult's law.

(1)A and B only
(2)B and C only
(3)A only
(4)A and C only

✓

Verified Against NTA Final Answer Key

Option (1) : A and B only

📚 Solutions Medium

📋 Given Parameters & Problem Setup

Statement A An ideal solution thus formed obeys Raoult's law throughout the composition range.

Statement B Mixture of chloroform and acetone shows negative deviation from Raoult's law.

Statement C Mixture of aniline and phenol shows positive deviation from Raoult's law.

⚡

The 30-Second Exam Hall Shortcut: ⚡ The Hydrogen Bonding Deviation Rule

⏱️ Save ~50 seconds

NEW intermolecular H-bonds formed upon mixing = NEGATIVE deviation ALWAYS!

1 Statement A: An ideal solution obeys Raoult's law across all concentrations -> TRUE (canonical definition).

2 Statement B: Chloroform (Cl₃C-H) forms a strong hydrogen bond with Acetone (>C=O). Stronger A-B attraction = lower vapor pressure = NEGATIVE deviation -> TRUE.

3 Statement C: Phenol (Ph-O-H) and Aniline (Ph-NH₂) form strong intermolecular H-bonds between phenolic -OH and basic -NH₂. This ALSO causes NEGATIVE deviation, NOT positive deviation! -> FALSE.

4 Therefore, only Statements A and B are correct -> Option (1) immediately!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Solutions textbook core examples: Both Chloroform + Acetone and Phenol + Aniline are classic textbook examples of NEGATIVE deviation.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Evaluate Statement A (Ideal Solution Definition)

An ideal solution is defined as a binary solution in which each component obeys Raoult's law over the entire range of concentration and temperature: P_A = P_A° x_A and P_B = P_B° x_B.

P_{\text{total}} = P_A^\circ x_A + P_B^\circ x_B \quad (\text{Obeys Raoult's law across all } x)

• Statement A is correct.

Step 2

Evaluate Statement B (Chloroform + Acetone Mixture)

Chloroform (CHCl₃) and acetone (CH₃COCH₃) molecules form intermolecular hydrogen bonds between the acidic hydrogen of chloroform and the carbonyl oxygen of acetone. Because A-B interactions are STRONGER than A-A and B-B interactions, vapor escaping tendency decreases, leading to lower vapor pressure than predicted by Raoult's law (Negative deviation).

\text{Cl}_3\text{C}-\text{H} \cdots \text{O}=\text{C}(\text{CH}_3)_2 \implies P_{\text{obs}} < P_{\text{Raoult}} \quad (\text{Negative Deviation})

• Δ_mix H < 0 and Δ_mix V < 0.
• Statement B is correct.

Step 3

Evaluate Statement C (Phenol + Aniline Mixture)

Phenol and aniline form strong intermolecular hydrogen bonds between the phenolic proton (-OH) and the lone pair on the nitrogen atom of aniline (-NH₂). This A-B interaction is significantly stronger than the individual intermolecular interactions. Consequently, the mixture shows NEGATIVE deviation from Raoult's law, NOT positive deviation.

\text{C}_6\text{H}_5-\text{O}-\text{H} \cdots \text{NH}_2-\text{C}_6\text{H}_5 \implies \text{Negative Deviation (NOT Positive)}

• Statement C is incorrect.

Step 4

Conclusion

Statements A and B only are correct.

\text{A: Correct, B: Correct, C: Incorrect} \implies \text{A and B only (Option 1)}

• Matches Option (1).

⭐

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:

Accurate. A is the canonical definition of an ideal solution; B correctly identifies negative deviation; C is false because phenol + aniline also shows negative deviation.

💡

Why this is airtight: None; precise recall of liquid-mixture thermodynamics.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Statement C is false and Statement A is correct.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming phenol + aniline shows positive deviation.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Overlooks that Statement B is completely true.

⚠️

Student Fallacy (Why candidates pick this trap): Doubting whether chloroform + acetone is a negative deviation system.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Statement C is false.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking acid-base liquid mixtures cause positive deviation.

⚠️

NTA Trap Alert: Misclassifying Phenol + Aniline Deviation

Students often know that Ethanol + Acetone shows positive deviation, and mistakenly think Phenol + Aniline does too. Phenol (acidic) and Aniline (basic) attract each other strongly, leading to NEGATIVE deviation!

🛡️ How to avoid the -1 mark: Acid + Base pairs (Phenol + Aniline, Chloroform + Acetone) ALWAYS show NEGATIVE deviation due to enhanced intermolecular attraction.

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Solutions Standard Benchmark

Core Scientific Principle Tested:

"Intermolecular attractions stronger than pure components (A-B > A-A, B-B) lead to negative deviation from Raoult's law."

Syllabus Focus: Ideal and non-ideal solutions, Raoult's law, positive and negative deviations

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Chloroform & Acetone, Phenol & Aniline: Negative deviation all down the line!

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NEET 2026 Chemistry Question 71 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ The Hydrogen Bonding Deviation Rule

Step-by-Step Rigorous Workflow & Mathematical Proof

Evaluate Statement A (Ideal Solution Definition)

Evaluate Statement B (Chloroform + Acetone Mixture)

Evaluate Statement C (Phenol + Aniline Mixture)

Conclusion

360° Option Elimination Engine Key Feature

NTA Trap Alert: Misclassifying Phenol + Aniline Deviation

Core NEET Syllabus Standard

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🔗 Related Questions — Solutions

Classification of Solutions: Solute and Solvent States

Highest Boiling Point of Aqueous Solutions (Effective Molality / Osmolarity)

Identification of Deviation from Raoult’s Law from Vapor Pressure Measurements

Henry’s Law Constant and Gas Solubility in Liquids

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