Q.On hydrolysis, which of the following carbohydrates gives only glucose? (A) Starch (B) Fructose (C) Lactose (D) Sucrose

The key idea is that hydrolysis breaks a carbohydrate into its constituent monosaccharides. The question asks for the one that yields only glucose — no other sugar.

• Starch is a polymer of glucose; on complete hydrolysis, it gives only glucose molecules.
• Fructose is already a monosaccharide — it does not hydrolyse further.
• Lactose is a disaccharide of glucose and galactose; hydrolysis gives both. …

The question asks which carbohydrate, when broken down by water (hydrolysis), produces only glucose as the final product. This is a test of your knowledge of the basic structure of common carbohydrates — specifically, which ones are homopolymers of glucose and which are heteropolymers or disaccharides made of different sugars.

Let’s recall the composition of each option:

1. Starch is a polysaccharide found in plants. It is made entirely of D-glucose units linked together by glycosidic bonds (α-1,4 and α-1,6 linkages in amylopectin). When you hydrolyse starch completely (using acid or enzymes), every bond breaks, and you are left with nothing but glucose molecules. So starch is a homopolymer of glucose.

2. Fructose is already a monosaccharide. Hydrolysis is not applicable to it in the same sense — it is already the simplest sugar unit. The question implies a carbohydrate that yields glucose upon hydrolysis, so fructose itself does not hydrolyse to give glucose. (It is an isomer of glucose, not a polymer.)

3. Lactose is a disaccharide made of one molecule of galactose and one molecule of glucose, linked by a β-1,4 bond. Hydrolysis of lactose gives both glucose and galactose — not glucose alone.

4. Sucrose is a disaccharide made of one molecule of glucose and one molecule of fructose, linked by an α-1,2 bond. Hydrolysis of sucrose gives both glucose and fructose — again, not glucose alone. …