Q.82 Chemistry ⭐ 360° Option Elimination Active

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NEET 2025 Chemistry Question 82 Solution

Topic: Biomolecules · Official NTA Booklet Code 45

Question

Sugar 'X' A. is found in honey. B. is a keto sugar. C. exists in α and β-anomeric forms. D. is laevorotatory. 'X' is:

✓

Verified Against NTA Final Answer Key

Option (2) : D-Fructose

📚 Biomolecules Easy

📋 Given Parameters & Problem Setup

Property A Found in honey (along with glucose)

Property B Is a keto sugar (ketohexose)

Property C Exists in α and β - anomeric forms (furanose ring)

Property D Is laevorotatory ([α]_D = -92.4°)

⚡

The 30-Second Exam Hall Shortcut: ⚡ Keto Sugar & Laevorotatory Match

⏱️ Save ~30 seconds

Clue B: "is a keto sugar" immediately eliminates D-Glucose (aldohexose), Maltose (disaccharide of glucose), and Sucrose! Clue D: "is laevorotatory" confirms D-Fructose (historically called LEVULOSE because [α]_D = -92.4°)! ⟹ D-Fructose!

1 Read Clue B: "Sugar X is a keto sugar." Glucose is an aldohexose. Maltose and sucrose are disaccharides. Fructose is the ONLY ketohexose among the options!

2 Read Clue D: "Sugar X is laevorotatory." D-Fructose is strongly laevorotatory with specific rotation [α]_D = -92.4° (hence its traditional name levulose), whereas D-glucose is dextrorotatory (+52.7°).

3 Read Clue C: "Exists in α and β - anomeric forms." Fructose forms cyclic hemiketal furanose structures (α-D-fructofuranose and β-D-fructofuranose).

4 Read Clue A: "Found in honey." Natural honey consists predominantly of fructose (~38%) and glucose (~31%).

5 All 4 properties unambiguously identify Sugar X as D-Fructose!

6 Select Option (2) in under 5 seconds!

🛡️

Why You Can 100% Trust This Shortcut: Furanose Ring Structure & Functional Groups of Fructose (NCERT Chemistry · Biomolecules).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Analyze Chemical Classification: Keto Sugar

Carbohydrates are classified as aldoses or ketoses based on the functional carbonyl group:

\text{D-Glucose: Aldohexose } (-\text{CHO at C1}), \quad \text{D-Fructose: Ketohexose } (>\text{C}=\text{O at C2})

• Maltose is a disaccharide composed of two α-D-glucose units.
• Sucrose is a non-reducing disaccharide composed of glucose and fructose.
• Therefore, among monosaccharides, only D-Fructose is a keto sugar.

Step 2

Evaluate Optical Activity (Laevorotatory Nature)

Examine optical rotation properties of D-monosaccharides:

[\alpha]_D^{20}(\text{D-Glucose}) = +52.7^\circ \text{ (Dextrorotatory)}, \quad [\alpha]_D^{20}(\text{D-Fructose}) = -92.4^\circ \text{ (Laevorotatory)}

• Because of its strong negative rotation, D-fructose is universally known as levulose.
• This property completely excludes D-glucose and matches D-fructose.

Step 3

Verify Anomeric Forms and Natural Occurrence in Honey

Cyclization of the C2 keto group with the C5 hydroxyl group produces a five-membered hemiketal furanose ring:

\text{Fructose} \rightleftharpoons \alpha\text{-D-(-)-fructofuranose} + \beta\text{-D-(-)-fructofuranose}

• Honey is nature’s richest source of free fructose.
• Thus Sugar X is unequivocally D-Fructose, matching Option (2).

⭐

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. D-Glucose is an aldo sugar (not keto) and is dextrorotatory (+52.7°).

⚠️

Student Fallacy (Why candidates pick this trap): Confusing glucose with fructose.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. Keto sugar, found in honey, exhibits α/β anomers, and is strongly laevorotatory.

💡

Why this is airtight: None; textbook mastery of carbohydrates.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Maltose is a disaccharide of two glucose units and is dextrorotatory.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking maltose is a simple keto sugar.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Sucrose is a disaccharide and dextrorotatory (+66.5°).

⚠️

Student Fallacy (Why candidates pick this trap): Confusing invert sugar with pure sucrose.

⚠️

NTA Trap Alert: Confusing Invert Sugar Hydrolysis with Pure Sugar Rotation

Sucrose upon hydrolysis becomes laevorotatory (invert sugar) because fructose (-92.4°) dominates glucose (+52.7°). But intact sucrose is DEXTROROTATORY (+66.5°). The standalone laevorotatory keto sugar itself is D-FRUCTOSE!

🛡️ How to avoid the -1 mark: Remember: Fructose = Keto sugar = Levulose (Laevorotatory)!

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Biomolecules Standard Benchmark

Core Scientific Principle Tested:

"D-Fructose is a laevorotatory ketohexose existing in α and β furanose forms."

Syllabus Focus: Structure and Properties of Monosaccharides: D-Fructose

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Keto + Laevo = Fructose (Levulose) in honey (Option 2)!

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NEET 2025 Chemistry Question 82 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Keto Sugar & Laevorotatory Match

Step-by-Step Rigorous Workflow & Mathematical Proof

Analyze Chemical Classification: Keto Sugar

Evaluate Optical Activity (Laevorotatory Nature)

Verify Anomeric Forms and Natural Occurrence in Honey

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Invert Sugar Hydrolysis with Pure Sugar Rotation

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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