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Which one of the following statements not true ?

1. Lactose contains α-glycosidic linkage between C1 of galactose and C4 of glucose.
2. Lactose (C12H22O11) is a disaccharide and it contains 8 hydroxyl groups.
3. On acid hydrolysis, lactose gives one molecule of D(+)-glucose and one molecule of D(+)-galactose.
4. Lactose is a reducing sugar and it gives Fehling's test.

Correct answer: Lactose contains α-glycosidic linkage between C1 of galactose and C4 of glucose.

Solution

In lactose the linkage between C1 of galactose and C4 of glucose is a beta-1,4-glycosidic bond, not alpha. The other statements (8 hydroxyl groups, hydrolysis to glucose + galactose, reducing sugar giving Fehling's test) are all true. So the untrue statement is the one claiming an alpha-linkage.

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