Question

Which is a reducing sugar 

• A. Galactose
• B. Gluconic acid
• C. β-methyl galactoside
• D. Sucrose

Answer 1

The Correct Option is A

A reducing sugar is one that has the ability to act as a reducing agent due to the presence of a free aldehyde group (-CHO) or a free ketone group (-C=O) in its structure. Reducing sugars undergo oxidation and reduce other substances in the process.

Let's analyze each of the given options:

• Galactose: Galactose is a monosaccharide that contains a free aldehyde group, making it capable of acting as a reducing sugar. It can be easily oxidized, thus participating in reactions such as the Benedict's test or Fehling's test, which are used to identify reducing sugars.
• Gluconic acid: This is a sugar acid resulting from the oxidation of glucose. It lacks a free aldehyde or ketone group because the aldehyde group on the glucose has been converted to a carboxylic acid group (-COOH), making it incapable of acting as a reducing sugar.
• β-Methyl galactoside: This is a glycoside form of galactose where the OH group at the anomeric carbon is replaced by a methoxy group (OCH₃), thus blocking the aldehyde function and preventing it from participating in oxidation-reduction reactions. Hence, it is not a reducing sugar.
• Sucrose: Sucrose is a disaccharide composed of glucose and fructose. In sucrose, the anomeric carbon of glucose forms a glycosidic bond with the anomeric carbon of fructose, resulting in no free aldehyde or keto group available for reduction, thus not a reducing sugar.

Based on the above analysis, the correct answer is:

Galactose, as it is a reducing sugar with a free aldehyde group that allows it to participate in reduction-oxidation reactions.