JEE Main 2022 · 29 July · evening · Single correct · +4 / −1
Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Amylose is insoluble in water.
Reason R: Amylose is a long linear molecule with more than 200 glucose units.
In the light of the above statements, choose the correct answer from the options given below.
- (a) Both A and R are correct and R is the correct explanation of A.
- (b) Both A and R are correct but R is NOT the correct explanation of A.
- (c) A is correct but R is not correct
- (d) A is not correct but R is correct.
Answer and solution
Answer (d) A is not correct but R is correct.
Solution
Chemistry ma’am · 4 steps
Remember the NCERT split of starch: amylose is the water-soluble part, amylopectin is the insoluble one.
- Starch has two parts. Starch is a polymer of α-D-glucose made of two components, amylose and amylopectin. They differ in chain shape and in how they behave in water.
Property Amylose Amylopectin Share of starch about 15 to 20% about 80 to 85% Chain shape long, unbranched, 200 to 1000 glucose units branched Linkages C1 to C4 glycosidic only C1 to C4 in the chain, C1 to C6 at branches In water soluble insoluble - Check A. The Assertion calls amylose insoluble in water. That is the property of amylopectin, not amylose, so A is not correct.
- Check R. Amylose is a long linear chain of 200 to 1000 α-D-glucose units, so it does have more than 200 units. R is correct.
- So. A is false and R is true, which is option (d).
The idea to keep. For starch, link the words in pairs: amylose goes with linear and water-soluble, amylopectin goes with branched and water-insoluble. Judge A and R one at a time before asking whether R explains A.
Answer from the NTA final answer key. Solution by PrepWiser.