Reducing property of monosaccharides is due to the presence of

Anomeric hydroxyl group

The correct answer is option 3. Anomeric hydroxyl group.

Cyclic hemiacetals exist in two anomeric forms, the alpha and beta forms. The alpha form has the free hydroxyl group on the anomeric carbon, while the beta form has the hydroxyl group in the ether linkage. Tollens' reagent and Fehling's reagent can both react with the free hydroxyl group on the anomeric carbon of a cyclic hemiacetal. This reaction opens the hemiacetal ring and converts the sugar into an aldehyde, which can then be oxidized by the reagent.

The oxidation reaction that occurs when Tollens' reagent or Fehling's reagent reacts with a cyclic hemiacetal is a redox reaction. The reagent is oxidized, while the sugar is reduced. In the case of Tollens' reagent, the silver ion in the reagent is oxidized to silver metal, which forms a precipitate. In the case of Fehling's reagent, the cupric ion in the reagent is oxidized to cuprous oxide, which also forms a precipitate.

The ability of Tollens' reagent and Fehling's reagent to react with cyclic hemiacetals is used to test for the presence of reducing sugars. Reducing sugars are sugars that have a free aldehyde or ketone group. When a reducing sugar reacts with Tollens' reagent or Fehling's reagent, the free aldehyde or ketone group is oxidized, and the characteristic precipitate is formed.