JEE Main 2021 · 27 July · evening · Single correct · +4 / −1
Compound A gives D-Galactose and D-Glucose on hydrolysis. The compound A is :
- (a) Amylose
- (b) Sucrose
- (c) Maltose
- (d) Lactose
Answer and solution
Answer (d) Lactose
Solution
Chemistry ma’am · 3 steps
Galactose is the giveaway: among these, only milk sugar has a galactose unit in it.
- Look at products. Hydrolysis breaks a carbohydrate into its monosaccharide units. So list the units each option is built from, and find the one that gives both galactose and glucose.
Compound Type Hydrolysis gives Amylose polysaccharide (part of starch) only α-D-glucose Sucrose disaccharide (cane sugar) D-glucose + D-fructose Maltose disaccharide (malt sugar) 2 units of D-glucose Lactose disaccharide (milk sugar) β-D-galactose + β-D-glucose - Linkage in lactose. In lactose, C1 of β-D-galactose is joined to C4 of glucose by a β-1,4 glycosidic link. Breaking this link releases one galactose and one glucose.
- So. Compound A is lactose, option (d).
The idea to keep. Learn each disaccharide by its two units. Sucrose is glucose plus fructose, maltose is glucose plus glucose, and lactose is galactose plus glucose. Galactose in the products always points to lactose.
Answer from the NTA final answer key. Solution by PrepWiser.