Q.121 Chemistry ⭐ 360° Option Elimination Active

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NEET 2020 Chemistry Question 121 Solution

Topic: Biomolecules · Official NTA Booklet Code E1

Question

Sucrose on hydrolysis gives:

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Verified Against NTA Final Answer Key

Option (3) : α-D-Glucose+β-D-Fructose

📚 Biomolecules Easy

📋 Given Parameters & Problem Setup

Disaccharide Sucrose (C12H22O11, cane sugar)

Reaction Aqueous acid or invertase-catalyzed hydrolysis

Question Objective Identify the exact anomeric forms of monosaccharide products

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The 30-Second Exam Hall Shortcut: ⚡ "Sucrose = α-D-Glucose (C1) linked to β-D-Fructose (C2)!"

⏱️ 20 seconds

Sucrose is a non-reducing disaccharide composed of an $\alpha$ -D-glucopyranosyl ring linked via a $C_1-C_2$ glycosidic bond to a $\beta$ -D-fructofuranosyl ring. Upon hydrolysis, it yields an equimolar mixture of $\alpha$ -D-Glucose and $\beta$ -D-Fructose! (Maltose gives two α-D-glucoses; Lactose gives β-D-galactose + β-D-glucose). Mark Option (3) in 5 seconds.

1 Structure of Sucrose: α-D-Glucopyranose (C1) joined to β-D-Fructofuranose (C2).

2 Hydrolysis reaction: C12H22O11 + H2O -> α-D-Glucose + β-D-Fructose.

3 Mixture undergoes inversion of specific rotation (Invert sugar).

4 Select Option (3) α-D-Glucose + β-D-Fructose.

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Why You Can 100% Trust This Shortcut: NCERT Chemistry · Biomolecules (Carbohydrates: Disaccharides - Sucrose & Invert Sugar)

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Molecular Composition of Sucrose

Sucrose is a common disaccharide that on hydrolysis with dilute acid or the enzyme invertase gives equimolar quantities of D-(+)-glucose and D-(-)-fructose: $\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \to \text{C}_6\text{H}_{12}\text{O}_6 \text{ (D-glucose)} + \text{C}_6\text{H}_{12}\text{O}_6 \text{ (D-fructose)}$

Step 2

Identify Specific Anomeric Stereochemistry

In sucrose, the two monosaccharide units are held together by a glycosidic linkage between $C_1$ of $\alpha$ -D-glucose and $C_2$ of $\beta$ -D-fructose. Since the reducing groups of glucose (hemiacetal) and fructose (hemiketal) are involved in glycosidic bond formation, sucrose is a non-reducing sugar.

Step 3

Hydrolysis Products

Cleavage of this glycosidic bond liberates the constituent monosaccharides in their original respective anomeric configurations: $\alpha$ -D-glucose and $\beta$ -D-fructose.

Step 4

Contrast with Maltose and Lactose

- Maltose hydrolyzes into two $\alpha$ -D-glucose units. - Lactose hydrolyzes into $\beta$ -D-galactose and $\beta$ -D-glucose.

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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; reverses the anomeric configurations of both sugars (it is alpha for glucose, beta for fructose).

⚠️

Student Fallacy (Why candidates pick this trap): Swapping alpha and beta anomers.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; sucrose contains one glucose and one fructose unit, not two glucose units (maltose yields glucose only).

⚠️

Student Fallacy (Why candidates pick this trap): Confusing sucrose with maltose or cellobiose.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Factually exact; sucrose is composed of α-D-glucopyranose and β-D-fructofuranose linked through C1-C2 glycosidic linkage.

💡

Why this is airtight: None; core carbohydrate biochemistry fact.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; sucrose does not yield two fructose units.

⚠️

Student Fallacy (Why candidates pick this trap): Arbitrary option.

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NTA Trap Alert: Mnemonic for Disaccharide Monomers

- Sucrose = α-D-Glucose + β-D-Fructose (Invert Sugar). - Maltose = α-D-Glucose + α-D-Glucose. - Lactose = β-D-Galactose + β-D-Glucose.

🛡️ How to avoid the -1 mark: Mnemonic: "Sucrose = Alpha Glucose + Beta Fructose"!

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Core NEET Syllabus Standard

Chemistry · Biomolecules Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Hydrolysis of Sucrose: Glycosidic Linkage between α-D-Glucose and β-D-Fructose

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Chemistry Question 121 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Sucrose = α-D-Glucose (C1) linked to β-D-Fructose (C2)!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Molecular Composition of Sucrose

Identify Specific Anomeric Stereochemistry

Hydrolysis Products

Contrast with Maltose and Lactose

360° Option Elimination Engine Key Feature

NTA Trap Alert: Mnemonic for Disaccharide Monomers

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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