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Chemistry Question 69 – JEE-MAIN 2026

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The incorrect statement from the following with respect to carbohydrates is :

Recall the definitions and properties of monosaccharides, oligosaccharides, and polysaccharides.

Step 1: Evaluate Statement 1: Monosaccharides as Reducing Sugars✦ Active

Monosaccharides possess free aldehyde or ketone groups (which can isomerize to aldehyde groups in alkaline medium). These groups can reduce Tollens' reagent or Fehling's solution. Therefore, all monosaccharides are reducing sugars. This statement is correct.

Step 2: Evaluate Statement 2: Hydrolysis of Oligosaccharides○ Expand

Oligosaccharides yield 2 to 10 monosaccharide units upon hydrolysis. These units can be identical (e.g., maltose yields two glucose units) or different (e.g., sucrose yields one glucose and one fructose unit; lactose yields one glucose and one galactose unit). Thus, the monosaccharide units obtained from hydrolysis of oligosaccharides are not always the same. This statement is incorrect.

💡 Teacher's Secret Hint

Remember common disaccharides like sucrose and lactose, which yield different monosaccharide units upon hydrolysis.

Step 3: Evaluate Statements 3 and 4○ Expand

Statement 3: Starch and cellulose are indeed polysaccharides, which are high molecular weight polymers composed of many monosaccharide units (typically hundreds to thousands). 'More than ten monosaccharide units' correctly describes a polysaccharide. This statement is correct.

Statement 4: D-(+)-glucose exists in aqueous solution as an equilibrium mixture of its open-chain aldehyde form and various cyclic hemiacetal forms (pyranose and furanose rings, specifically α-D-glucopyranose and β-D-glucopyranose). This equilibrium is responsible for properties like mutarotation. This statement is correct.

💡 Teacher's Secret Hint

The equilibrium between open-chain and cyclic forms is a fundamental aspect of monosaccharide chemistry.

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