Given below are two statements : In the light of the above statements, choose the correct answer from the options given below :
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
Answer
(4) Statement I is false but Statement II is true
Solution
A sugar is reducing when it has a free hemiacetal/hemiketal –OH at an anomeric carbon (it can open to an aldehyde and reduce Tollens'/Fehling's reagent).
Maltose: C1 of the first α-D-glucose is linked to C4 of the second glucose (α-1,4 glycosidic link); C1 of the second glucose still carries a free –OH.
⇒ As per NCERT, maltose is a reducing sugar ⇒ Statement I is false.
Lactose: C1 of β-D-galactose is linked to C4 of β-D-glucose; C1 of the glucose unit has a free –OH.
⇒ Lactose is a reducing sugar ⇒ Statement II is true.
(Sucrose, with both anomeric carbons joined, is the common non-reducing disaccharide.)
Answer: (4)