Chemistry · Biomolecules · chapter 10 of 10

Class 12 Chemistry Chapter 10: Biomolecules Assertion-reason questions with answers

2 assertion-reason questions on Biomolecules, each with its answer and the reason, written from the NCERT chapter. For the CBSE board, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): Sucrose does not reduce Fehling's solution. Reason (R): In sucrose the glycosidic linkage joins C1 of α-D-glucose to C2 of β-D-fructose, so the reducing groups of both units are bonded.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true, and R explains A: with the aldehydic group of glucose and the ketonic group of fructose both used in the linkage, no free reducing group is left, so sucrose is non-reducing.

Question 2
Assertion (A): Amino acids are colourless crystalline solids with high melting points. Reason (R): Except glycine, all naturally occurring α-amino acids are optically active.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true, but R does not explain A. The high melting points come from salt-like behaviour, the acidic –COOH and basic –NH₂ being in the same molecule; optical activity comes from the asymmetric α-carbon and has nothing to do with melting point.

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