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, because it can then open to an aldehyde and reduce Tollens'/Fehling's reagent.
In maltose, C1 of the first α-D-glucose is linked to C4 of the second glucose (α-1,4 glycosidic link), while C1 of the second glucose still carries a free –OH. So, as per NCERT, maltose is a reducing sugar and Statement I is false.
In lactose, C1 of β-D-galactose is linked to C4 of β-D-glucose, and C1 of the glucose unit has a free –OH, so lactose is a reducing sugar and Statement II is true.
(Sucrose, with both anomeric carbons joined, is the common non-reducing disaccharide.)
Answer: (4)